Fix missing task file input declaration (#35)

Description
===========

The `CopySpec` allows to define source path declarations from multiple
sources. If the input is a task or a configuration gradle would normally
execute the tasks to produce the connected artifacts. As pointed out in
[issue 30] the publish tasks missed a declaration step to tell gradle to
connect these input/outputs.

Changes
=======

![FIX] missing file input declaration

[issue 30]: #30

src/integrationTest/groovy/wooga/gradle/github/GithubPublishAssetsIntegrationSpec.groovy

@@ -20,6 +20,7 @@ package wooga.gradle.github
 import spock.genesis.Gen
 import spock.genesis.transform.Iterations
 import spock.lang.IgnoreIf
+import spock.lang.Issue
 import spock.lang.Shared
 import spock.lang.Unroll
 
@@ -402,4 +403,118 @@ class GithubPublishAssetsIntegrationSpec extends GithubPublishIntegrationWithDef
         tagName = "v0.${tag}.0-GithubPublishAssetsIntegrationSpec"
 
     }
+
+    @Issue("https://github.com/wooga/atlas-github/issues/30")
+    def "executes depended tasks and fetches task outputs"() {
+        given: "a task that produces an output"
+        buildFile << """
+        task createOutput {
+            outputs.file("build/outputs/${assetName}")
+
+            doLast {
+                def outputFile = file("build/outputs/${assetName}")
+                outputFile.parentFile.mkdirs()
+                outputFile.text = "${assetContent}"
+            }
+        }
+        """.stripIndent()
+
+        and: "a publish task which from points to the custom task"
+        buildFile << """
+            task testPublish(type:wooga.gradle.github.publish.tasks.GithubPublish) {
+                tagName = "$tagName"
+                releaseName = "$tagName" 
+
+                from(createOutput)
+            }
+        """
+
+        when:
+        def result = runTasksSuccessfully("testPublish")
+
+        then:
+        result.wasExecuted("createOutput")
+        def release = getRelease(tagName)
+        def assets = release.getAssets()
+        assets.size() == 1
+        assets[0].name == assetName
+
+        where:
+        tagName = "v0.8.0-GithubPublishIntegrationSpec"
+        assetName = "list.txt"
+        assetContent = "Custom content"
+    }
+
+    @Issue("https://github.com/wooga/atlas-github/issues/30")
+    def "executes depended tasks through configuration"() {
+        given: "a subproject that produces an artifact"
+        addSubproject("sub", """
+        plugins {
+            id "base"
+        }
+
+        def outputFile = file("build/outputs/${assetName}")
+
+        task createOutput {            
+            doLast {
+                outputFile.parentFile.mkdirs()
+                outputFile.text = "${assetContent}"
+            }
+        }
+
+        assemble.dependsOn createOutput
+
+        configurations {
+            output
+        }
+
+        configurations['default'].extendsFrom(configurations.output)
+
+        artifacts {
+            output(outputFile) {
+                builtBy project.tasks.createOutput
+            }
+        }
+
+        """.stripIndent())
+
+        and: "a dependency to the sub project artifact"
+        buildFile << """
+
+        configurations {
+            sub
+        }
+
+        dependencies {
+            sub project(':sub')
+        }
+
+        """.stripIndent()
+
+        and: "a publish task which from points to a configuration"
+        buildFile << """
+            task testPublish(type:wooga.gradle.github.publish.tasks.GithubPublish) {
+                tagName = "$tagName"
+                releaseName = "$tagName" 
+
+                from(configurations.sub)
+            }
+        """
+
+        when:
+        def result = runTasksSuccessfully("testPublish")
+
+        then:
+        result.wasExecuted(":sub:createOutput")
+        def release = getRelease(tagName)
+        def assets = release.getAssets()
+        assets.size() == 1
+        assets[0].name == assetName
+
+        where:
+        tagName = "v0.9.0-GithubPublishIntegrationSpec"
+        assetName = "output.txt"
+        assetContent = "Custom content"
+
+    }
 }

src/main/groovy/wooga/gradle/github/publish/tasks/GithubPublish.groovy

@@ -21,7 +21,9 @@ import groovy.io.FileType
 import groovy.json.JsonSlurper
 import org.apache.commons.io.FileUtils
 import org.gradle.api.Action
+import org.gradle.api.Buildable
 import org.gradle.api.GradleException
+import org.gradle.api.Task
 import org.gradle.api.file.CopySpec
 import org.gradle.api.file.FileTreeElement
 import org.gradle.api.logging.Logger
@@ -339,6 +341,7 @@ class GithubPublish extends AbstractGithubTask implements GithubPublishSpec {
      */
     @Override
     GithubPublish from(Object... sourcePaths) {
+        this.inputs.files(sourcePaths)
         assetsCopySpec.from(sourcePaths)
         processAssets = true
         this
@@ -366,6 +369,7 @@ class GithubPublish extends AbstractGithubTask implements GithubPublishSpec {
      */
     @Override
     GithubPublish from(Object sourcePath, Action<? super CopySpec> configureAction) {
+        this.inputs.files(sourcePath)
         assetsCopySpec.from(sourcePath, configureAction)
         processAssets = true
         this