clang-format: [JS] Support more regex literals.

Previously a regex-literal containing "/*" would through clang-format
off, e.g.:
  var regex = /\/*$/;

Would lead to none of the following code to be formatted.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@220860 91177308-0d34-0410-b5e6-96231b3b80d8