build: ignore proto files in test coverage (#202)

Author: JustinBeckwith

packages/google-cloud-oslogin/.nycrc

@@ -10,6 +10,7 @@
     "**/samples",
     "**/scripts",
     "**/src/**/v*/**/*.js",
+    "**/protos",
     "**/test",
     ".jsdoc.js",
     "**/.jsdoc.js",