0.7.4 released

Changes:

• It's no longer a requirement that Java/Android plugins are applied before the protobuf plugin. The plugins can be applied in arbitrary order.
• The Gradle plugins { } DSL is now supported, e.g.,

plugins {
  id "java"
  id "com.google.protobuf" version "0.7.4"
}

• Requires at least Gradle 2.4 and Java 7