Updated .gitignore to ignore isolate_deps_dir.

BUG=
R=kjellander@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/46909004

Cr-Commit-Position: refs/heads/master@{#9003}
diff --git a/.gitignore b/.gitignore
index 467e0e7..e173e64 100644
--- a/.gitignore
+++ b/.gitignore
@@ -45,6 +45,7 @@
 /chromium/src
 /google_apis
 /gyp-mac-tool
+/isolate_deps_dir
 /links
 /links.db
 /net