move protobufjs to devdeps

Author: Feiyang1

packages/firestore/package.json

@@ -33,7 +33,6 @@
     "@firebase/webchannel-wrapper": "0.2.21",
     "@grpc/proto-loader": "^0.5.0",
     "@firebase/util": "0.2.20",
-    "protobufjs": "6.8.8",
     "grpc": "1.20.3",
     "tslib": "1.9.3"
   },
@@ -66,6 +65,7 @@
     "npm-run-all": "4.1.5",
     "nyc": "14.1.0",
     "prettier": "1.17.0",
+    "protobufjs": "6.8.8",
     "rollup": "1.11.0",
     "rollup-plugin-copy-assets": "1.1.0",
     "rollup-plugin-node-resolve": "4.2.3",

packages/firestore/src/platform_node/load_protos.ts

@@ -18,6 +18,7 @@
 import * as protoLoader from '@grpc/proto-loader';
 import * as grpc from 'grpc';
 import * as path from 'path';
+// eslint-disable-next-line import/no-extraneous-dependencies, only used in tests
 import * as ProtobufJS from 'protobufjs';
 
 /** Used by tests so we can match @grpc/proto-loader behavior. */