Enforce a release is made with JDK 1.7 (and not w/ 1.8+)
Enforce a release is made with JDK 1.7 (and not w/ 1.8+)

Motivations:

JDK 1.8 adds default methods to collections classes that reference
classes that don't exist in JDK 7. That's binary compatible,
but not source compatible.

Modifications:

Enforce JDK version to be 1.7.* when releasing

Result:

Fixes #3548

yipen9/netty,purplefox/netty-4.0.2.8-hacked,imangry/netty-zh,imangry/netty-zh,yipen9/netty,purplefox/netty-4.0.2.8-hacked,yipen9/netty,imangry/netty-zh,chanakaudaya/netty,chanakaudaya/netty,purplefox/netty-4.0.2.8-hacked,imangry/netty-zh,chanakaudaya/netty,yipen9/netty,imangry/netty-zh,chanakaudaya/netty,purplefox/netty-4.0.2.8-hacked,chanakaudaya/netty