Make clang-tidy-diff.py py3-compatible.

llvm-svn: 211834
diff --git a/clang-tools-extra/clang-tidy/tool/clang-tidy-diff.py b/clang-tools-extra/clang-tidy/tool/clang-tidy-diff.py
index 14ee0d6..aee6ab7 100755
--- a/clang-tools-extra/clang-tidy/tool/clang-tidy-diff.py
+++ b/clang-tools-extra/clang-tidy/tool/clang-tidy-diff.py
@@ -92,7 +92,7 @@
       lines_by_file.setdefault(filename, []).append([start_line, end_line])
 
   if len(lines_by_file) == 0:
-    print "No relevant changes found."
+    print("No relevant changes found.")
     sys.exit(0)
 
   line_filter_json = json.dumps(