FORGE-1096 Fixed spurious ArrayIndexOutOfBoundsException.

The exception was thrown on rewriting the CompilationUnit, and
was most likely caused due to use of a lower source level.

Setting the source level to 1.7 gets rid of the exception.
Merge pull request #8 from VineetReynolds/FORGE-1096

FORGE-1096 Fixed spurious ArrayIndexOutOfBoundsException.