Add third_party/libyuv to .gitignore.

Review URL: http://webrtc-codereview.appspot.com/290010

git-svn-id: http://webrtc.googlecode.com/svn/trunk@1065 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/.gitignore b/.gitignore
index ec61a78..1896c63 100644
--- a/.gitignore
+++ b/.gitignore
@@ -44,6 +44,7 @@
 /third_party/libjpeg
 /third_party/libjpeg_turbo
 /third_party/libvpx
+/third_party/libyuv
 /third_party/llvm-build
 /third_party/protobuf
 /third_party/valgrind