clang-format: [JS] consistenly format enums.

Summary: Previously, const enums would get formatted differently because the modifier was not recognized.

Reviewers: djasper

Subscribers: klimek, cfe-commits

Differential Revision: https://reviews.llvm.org/D36144

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@309703 91177308-0d34-0410-b5e6-96231b3b80d8