clang-format: Fix Allman brace breaking of enums.

Before:
  enum Side
  { LEFT,
    RIGHT };

After:
  enum Side
  {
    LEFT,
    RIGHT
  };

This fixes llvm.org/PR19911.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@210011 91177308-0d34-0410-b5e6-96231b3b80d8