Fix POLICIES typo

POLICIES.md

     `throw new UnsupportedOperationException("Delete this statement and write your own implementation.");`
 > - Exercises 21+: provide no stubs by default, but either (1) add hints to the HINTS.md file (which gets merged into the README.md for the exercise) or (2) provide stubs as in exercises 1-20 for exercises that demand complicated method signatures.
 
-References: [[1](https://github.com/exercism/java/issues/178)], [[2](https://github.com/exercism/java/pull/683#discussion_r125506930))
+References: [[1](https://github.com/exercism/java/issues/178)], [[2](https://github.com/exercism/java/pull/683#discussion_r125506930)]
 
 ### Do not make user-facing classes `final`