Updating opus in .gitignore

BUG=none
TEST=git status in a git-svn checkout.

Review URL: https://webrtc-codereview.appspot.com/965011

git-svn-id: http://webrtc.googlecode.com/svn/trunk@3051 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/.gitignore b/.gitignore
index 4d64284..b82f30b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -56,7 +56,7 @@
 /third_party/libyuv
 /third_party/llvm-build
 /third_party/oauth2
-/third_party/opus/source
+/third_party/opus
 /third_party/protobuf
 /third_party/valgrind
 /third_party/yasm