fix(example-rpc-server): mocha opts, mark as private (#923)

* fix: mocha opts in example-rpc-server

Use the new "mocha.opts" instead of no-longer-available "mocha.ts.opts"

* fix: mark example-rpc-server as private

Set `private` flag in package.json so that `lerna publish`
won't push it to npm.

packages/example-rpc-server/package.json

@@ -2,6 +2,7 @@
   "name": "@loopback/example-rpc-server",
   "version": "4.0.0-alpha.0",
   "description": "A basic RPC server using a made-up protocol.",
+  "private": true,
   "keywords": [
     "loopback-application",
     "loopback"
@@ -24,7 +25,7 @@
     "tslint": "lb-tslint",
     "tslint:fix": "npm run tslint -- --fix",
     "pretest": "npm run clean && npm run build:current",
-    "test": "lb-dist mocha --opts node_modules/@loopback/build/mocha.ts.opts DIST/test",
+    "test": "lb-dist mocha --opts node_modules/@loopback/build/mocha.opts DIST/test",
     "posttest": "npm run lint",
     "start": "npm run build && node .",
     "prepare": "npm run build"