[clang-doc] Fix paths of js in import tags

HTML requires posix-style paths.

Differential Revision: https://reviews.llvm.org/D65827

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@368087 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed