clang-format: [JS] Fix bug in type colon detection.

Before, this couldn't be formatted at all:
  class X {
    subs = {
      'b': {
        'c': 1,
      },
    };
  }

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@238907 91177308-0d34-0410-b5e6-96231b3b80d8