Add @plugins_npm for plugin dependencies

Change-Id: I0139febad10c8073bfab3fa324a2a8ac2a25d8d6
diff --git a/.gitignore b/.gitignore
index 3a5d28b..bcafbb4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -31,6 +31,8 @@
 /node_modules/
 /package-lock.json
 /plugins/*
+!/plugins/package.json
+!/plugins/yarn.lock
 !/plugins/BUILD
 !/plugins/codemirror-editor
 !/plugins/commit-message-length-validator