NOJIRA: Pin version of Error Prone core used
NOJIRA: Pin version of Error Prone core used

error prone core 2.1 is throwing

``` log
java.lang.ClassCastException: com.sun.tools.javac.tree.JCTree$JCExpressionStatement cannot be cast to com.sun.source.tree.BlockTree
```

reverting back to previous minor release resolves the issue

phillips1021/uPortal,GIP-RECIA/esco-portail,Jasig/uPortal,groybal/uPortal,GIP-RECIA/esup-uportal,jonathanmtran/uPortal,mgillian/uPortal,bjagg/uPortal,Jasig/uPortal,groybal/uPortal,groybal/uPortal,ChristianMurphy/uPortal,phillips1021/uPortal,jonathanmtran/uPortal,mgillian/uPortal,cousquer/uPortal,jonathanmtran/uPortal,ChristianMurphy/uPortal,Jasig/uPortal,ChristianMurphy/uPortal,phillips1021/uPortal,GIP-RECIA/esup-uportal,GIP-RECIA/esco-portail,groybal/uPortal,GIP-RECIA/esup-uportal,phillips1021/uPortal,cousquer/uPortal,groybal/uPortal,bjagg/uPortal,mgillian/uPortal,cousquer/uPortal,GIP-RECIA/esup-uportal,phillips1021/uPortal,GIP-RECIA/esco-portail,GIP-RECIA/esup-uportal,bjagg/uPortal