Fix clang-format output during linting

Instead of printing a binary object, treat the output of clang-format
as a utf-8 string.

b/190743862

Change-Id: I596d223792597f8157fdee2d75773131cc858c9a

packager/tools/git/check_formatting.py

@@ -52,7 +52,7 @@
       b'no modified files to format\n',
       b'clang-format did not modify any files\n'
   ]:
-    print(output)
+    print(output.decode('utf-8'))
     print()
     print('Code style is not correct. Please run {}.'.format(' '.join(command)))
     print()