Remove 1.6 JVM compliance: getting the 1.7 from top pom.xml
Remove 1.6 JVM compliance: getting the 1.7 from top pom.xml

The top-level pom.xml already defines Java 1.7 as the source
and binary compliance level: this change aligns the plugin to the top
level setting.

Change-Id: I819c830f7eb5d9fc509183ea961cb192e6627786

cjh1/github-plugin,cybojenix/github-plugin,GerritCodeReview/plugins_github,Kanth7686/TestInfoblox,thewtex/gerrit-plugins-github,cjh1/github-plugin,GerritCodeReview/plugins_github,cybojenix/github-plugin,GerritCodeReview/plugins_github,cybojenix/github-plugin,mohitsethi/gerrit_github,thewtex/gerrit-plugins-github,mohitsethi/gerrit_github,Kanth7686/TestInfoblox,jdoe123/plugins-github,Kanth7686/TestInfoblox,jdoe123/plugins-github