Fix clang-format-diff.py script.

llvm-svn: 179377
diff --git a/clang/tools/clang-format/clang-format-diff.py b/clang/tools/clang-format/clang-format-diff.py
index 16c6ad21..afed40f 100755
--- a/clang/tools/clang-format/clang-format-diff.py
+++ b/clang/tools/clang-format/clang-format-diff.py
@@ -65,7 +65,7 @@
     text = f.read()
   command = [binary, '-offset', str(offset), '-length', str(length)]
   if style:
-    command.append('-style', style)
+    command.extend(['-style', style])
   p = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE,
                        stdin=subprocess.PIPE)
   stdout, stderr = p.communicate(input=text)