Update build.gradle

- Update MinecraftForge version from 1047 to 1057
- Update ForgeGradle version from 1.1-SNAPSHOT to 1.2-SNAPSHOT
- Update Gradle-Cobertura-Plugin from 2.2.2 to 2.2.4
- Update Coveralls-Gradle-Plugin from 0.2.4 to 0.4.0
- Fixed Javadoc generation issue caused by Addon.java

Signed-off-by: Steven Downer <grinch@outlook.com>