clang-format: [ObjC] Fix method expression detection.

Before:
  return (a)[foo bar : baz];

After:
  return (a)[foo bar:baz];

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@219919 91177308-0d34-0410-b5e6-96231b3b80d8