fix(deps): update dependency @grpc/proto-loader to ^0.3.0 (#269)

Author: renovate[bot]

packages/packages/google-gax/package-lock.json

@@ -8,7 +8,7 @@
     "build/src"
   ],
   "dependencies": {
-    "@grpc/proto-loader": "^0.1.0",
+    "@grpc/proto-loader": "^0.3.0",
     "duplexify": "^3.6.0",
     "extend": "^3.0.1",
     "globby": "^8.0.1",