BREAKING: Bump metro-bundler to v0.21.0

Summary:
`metro-bundler` v0.21 contains a rewritten bundling mechanism, with simplified logic and much faster rebuild times, called delta bundler. This release contains a couple of breaking changes:

* Now, when using a custom transformer, the list of additional babel plugins to apply are passed to the `transform()` method. These are used in non-dev mode for optimization purposes (Check 367a5f5db8 (diff-40653f0c822ac59a5af13d5b4ab31d84) to see how to handle them from the transformer).
* Now, when using a custom transformer outputting `rawMappings`, the transformer does not need to call the `compactMappings` method before returning (check d74685fd1d (diff-40653f0c822ac59a5af13d5b4ab31d84) for more info).
* We've removed support for two config parameters: `postProcessModules` and `postProcessBundleSourcemap`.

Reviewed By: davidaurelio

Differential Revision: D6186035

fbshipit-source-id: 242c5c2a954c6b9b6f339d345f888eaa44704579

lerna.json

@@ -1,5 +1,5 @@
 {
-  "version": "0.20.0",
+  "version": "0.21.0",
   "lerna": "2.0.0-rc.5",
   "npmClient": "yarn",
   "packages": [

packages/metro-bundler/package.json

@@ -1,5 +1,5 @@
 {
-  "version": "0.20.0",
+  "version": "0.21.0",
   "name": "metro-bundler",
   "description": "🚇 The JavaScript bundler for React Native.",
   "main": "src/index.js",

packages/metro-bundler/src/Server/index.js

@@ -98,7 +98,6 @@ export type Options = {|
   +sourceExts: ?Array<string>,
   +transformCache: TransformCache,
   transformModulePath?: string,
-  useDeltaBundler?: boolean, // TODO: remove this, since it's no longer used
   watch?: boolean,
   workerPath: ?string,
 |};