[scripts] Update git-clang-format

Old git-clang-format was python2 compatible only.
Support for python2 is getting slowly away from modern distro.

This change sync git-clang-format from https://github.com/llvm-mirror/clang/blob/aa231e4be75ac4759c236b755c57876f76e3cf05/tools/clang-format/git-clang-format
which is python2 and python3 compatible.