Groovy jar - Use Java 7 version

[pickypg]

Now that we require Java 7, we can get invokedynamic benefits by using the Java 7 version of Groovy 2.x.

The change requires using a different Groovy jar geared specifically for Java 7. It's important to note their warning (taken verbatim from the above link):

All JDK 7 versions ranging from 7u21 to 7u55 are buggy with regards to invokedynamic. If you plan to use invokedynamic support, make sure you either use 7u60 or JDK 8.

This should help to speed up scripting support without any effort.

Thanks to Robert and Uwe for pointing it out.

[nik9000]

This would scratch 7u25 from the list of viable Java versions for Elasticsearch I think. Probably worth thinking about.

[rmuir]

7u25 is pretty ancient, the jre technically "expired" over a year ago. The change should go in 2.0 for sure.

[s1monw]

+1 for going for a newer JVM here I think the benefits are worth it!