gofrontend: add .clang-format to .gitignore file

Change-Id: I4be4a57d6b8d355cacce738864f924b1153983ed
Reviewed-on: https://go-review.googlesource.com/c/144417
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/.gitignore b/.gitignore
index 8229066..d54756d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
 *~
 *.pyc
 last-change
+.clang-format
\ No newline at end of file