[clang-format] Fix indent of 'key <...>' and 'key {...}' in text protos

Summary:
This patch fixes the indentation of the code pattern `key <...>`and `key {...}` in text protos.
Previously, such line would be alinged depending on the column of the previous
colon, which usually indents too much.

I'm gonna go ahead and commit this since it's a straightforward bugfix.

Reviewers: djasper, klimek

Subscribers: klimek, cfe-commits

Differential Revision: https://reviews.llvm.org/D36143

llvm-svn: 309941