Update maven-plugin-api

[moose-byte]

My team has a project that uses maven-karma-plugin. We specify a language level of Java 1.7. There is a warning produced during the build from a dependency deep within our dependency tree.

Warning:java: Supported source version 'RELEASE_6' from annotation processor 'org.sonatype.guice.bean.scanners.index.SisuIndexAPT6' less than -source '1.7'

Current dependency Tree

SisuIndexAPT6 is the culprit because it specifies SourceVersion.RELEASE_6

The latest maven-plugin-api uses a newer version of this library, which does not specify a language level.

Upgrading the dependency allows the library to be run in JVMs greater than 1.6 without warnings.

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[moose-byte]

I signed it!

[googlebot]

CLAs look good, thanks!

[moose-byte]

Travis is failing because it could not find a .travis.yml or Rakefile. I don't see these files in the master branch, so I'm not sure how to proceed.