[coroutines] Add syntax coloring to examples in Coroutines.rst

Subscribers: EricWF

Differential Revision: https://reviews.llvm.org/D31699

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@299517 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed