Ignore node_modules inside of polygerrit-ui and app.

I'm not sure why this wasn't there before, but this makes using `ag`
much nicer.

Release-Notes: skip
Change-Id: I3aa5d402967cffe97cf8a619800a4baaed47060b

.gitignore

diff --git a/.gitignore b/.gitignore
index 53bc9f6..0bbcaba 100644
--- a/.gitignore
+++ b/.gitignore
@@ -31,6 +31,8 @@
 /infer-out
 /local.properties
 /node_modules/
+/polygerrit-ui/node_modules/
+/polygerrit-ui/app/node_modules/
 /package-lock.json
 /plugins/*
 /polygerrit-ui/coverage/