Temporary fix for memory leak within antlr.

The antlr team have plans in the future to enhance the caching mechanism.
In the meantime, this workaround will clean the cache for each
instantiation. There may be performance implications, but certainly better
than crashing.

https://github.com/antlr/antlr4/issues/499
Merge branch 'memory-leak'
Merge branch 'master' into develop
Merge branch 'develop' into java8

Conflicts:
	src/main/java/com/github/antlrjavaparser/JavaParser.java