Merge pull request #13936 from grpc/copyright-objc++

Check copyright of Objective-C++ source files
diff --git a/tools/distrib/check_copyright.py b/tools/distrib/check_copyright.py
index 8f782e0..0eb2cbe 100755
--- a/tools/distrib/check_copyright.py
+++ b/tools/distrib/check_copyright.py
@@ -48,6 +48,7 @@
     '.cc': r'\s*(?://|\*)\s*',
     '.h': r'\s*(?://|\*)\s*',
     '.m': r'\s*\*\s*',
+    '.mm': r'\s*\*\s*',
     '.php': r'\s*\*\s*',
     '.js': r'\s*\*\s*',
     '.py': r'#\s*',