Fix proto-loader declaration in grpc-js devDependencies

Author: murgatroid99

packages/grpc-js/package.json

@@ -15,7 +15,7 @@
   "types": "build/src/index.d.ts",
   "license": "Apache-2.0",
   "devDependencies": {
-    "@grpc/proto-loader": "../proto-loader",
+    "@grpc/proto-loader": "file:../proto-loader",
     "@types/gulp": "^4.0.6",
     "@types/gulp-mocha": "0.0.32",
     "@types/lodash": "^4.14.186",