Bump to v4 (#278)

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## What
Bump Android SDK to the new Major 4 version. 
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## How
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Should only be merged after #277

README.md

@@ -1,4 +1,4 @@
-# Forage Android SDK (`v3.9.0`)
+# Forage Android SDK (`v4.0.0`)
 
 You can use the Forage Android SDK to process online-only and/or Terminal POS EBT payments. The SDK provides UI components known as Forage Elements and associated methods that perform payment operations.
 

forage-android/build.gradle

@@ -10,7 +10,7 @@ apply plugin: ShadowAarDependenciesPlugin
 
 ext {
     PUBLISH_GROUP_ID = 'com.joinforage'
-    PUBLISH_VERSION = '3.9.0'
+    PUBLISH_VERSION = '4.0.0'
     PUBLISH_ARTIFACT_ID = 'forage-android'
     PUBLISH_DESCRIPTION = 'Forage Android SDK'
     PUBLISH_URL = 'https://github.com/teamforage/forage-android-sdk'