[clang-format] append newline after code when inserting new headers at the end...

[clang-format] append newline after code when inserting new headers at the end of the code which does not end with newline.

Summary:
append newline after code when inserting new headers at the end of the
code which does not end with newline.

Reviewers: djasper

Subscribers: cfe-commits, klimek

Differential Revision: https://reviews.llvm.org/D21026

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@283330 91177308-0d34-0410-b5e6-96231b3b80d8