Fixing CLI to pass "sourcemap-output" option to bundler.

Summary:
Currently, the CLI is not passing the sourceMapURL option to the bundler, so source maps are output as "null".
Closes https://github.com/facebook/react-native/pull/5288

Reviewed By: svcscm

Differential Revision: D2828092

Pulled By: androidtrunkagent

fb-gh-sync-id: 2e464ddf65f0d4fcbff3c50281391cb30b5c799c

local-cli/bundle/buildBundle.js

@@ -33,6 +33,7 @@ function buildBundle(args, config, output = outputBundle) {
 
     const requestOpts = {
       entryFile: args['entry-file'],
+      sourceMapUrl: args['sourcemap-output'],
       dev: args.dev,
       minify: !args.dev,
       platform: args.platform,