Setup Continuous Delivery

Summary:
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**Summary**
As we discussed on Discord channel on Nov 6th, this PR adds appropriate hooks to CircleCI in order to deploy successful builds (on master branch) to `npm` using tag that has been assigned to the latest commit.

This is how deployment process should look like:
Once you want to deploy, push a new tag to master. That will trigger a deployment script on CI. [According to CircleCI documentation](https://circleci.com/docs/1.0/npm-continuous-deployment/), the best way is to use
```
npm version x.y.z
```
in order to update package version and create git tag.  Then, you can push your code using
```
git push --follow-tags
```
After successful build, a new version will be released.

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**Test plan**
Not sure if there is a way to properly test it before the merge. I think the only way is to merge it in, setup NPM_TOKEN env variable and try to create a new version by running build on CI. Please, let me know if you see alternative scenarios.

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Closes https://github.com/facebook/metro-bundler/pull/88

Reviewed By: BYK, cpojer

Differential Revision: D6332813

Pulled By: rafeca

fbshipit-source-id: 1902afa8eb77a59e813cefc8e7f650a0106edfef

circle.yml

@@ -1,28 +1,82 @@
-machine:
-  environment:
-    YARN_VERSION: 0.24.3
-    PATH: "${PATH}:${HOME}/.yarn/bin:${HOME}/${CIRCLE_PROJECT_REPONAME}/node_modules/.bin"
-  node:
-    version: 8
-dependencies:
-  pre:
-    - |
-      if [[ ! -e ~/.yarn/bin/yarn || $(yarn --version) != "${YARN_VERSION}" ]]; then
-        curl -o- -L https://yarnpkg.com/install.sh | bash -s -- --version $YARN_VERSION
-      fi
-    - nvm install 4
-    - nvm install 6
+aliases:
+  - &restore-cache
+    keys:
+      - dependencies-{{ .Branch }}-{{ checksum "package.json" }}
+      # Fallback in case checksum fails
+      - dependencies-{{ .Branch }}-
 
-  cache_directories:
-    - ~/.yarn
-    - ~/.cache/yarn
-  override:
-    - yarn install --no-progress
-test:
-  override:
-    - nvm alias default 6
-    - yarn run test-ci
-    - nvm alias default 4
-    - yarn run test-ci
-    - nvm alias default 8
-    - yarn run test-ci
+  - &save-cache
+    paths:
+      - node_modules
+    key: dependencies-{{ .Branch }}-{{ checksum "package.json" }}
+
+  - &deploy
+    working_directory: packages/metro-bundler
+    steps:
+      - run: npm run prepare-release
+      - run: npm publish
+      - run: npm run cleanup-release
+
+version: 2
+jobs:
+  test-node-9:
+    working_directory: ~/metro-bundler/packager/metro-bundler
+    docker:
+      - image: circleci/node:9
+    steps:
+      - checkout
+      - restore-cache: *restore-cache
+      - run: yarn --no-progress
+      - save-cache: *save-cache
+      - run: yarn run test-ci
+
+  test-node-8:
+    working_directory: ~/metro-bundler/packager/metro-bundler
+    docker:
+      - image: circleci/node:8
+    steps:
+      - checkout
+      - restore-cache: *restore-cache
+      - run: yarn --no-progress
+      - save-cache: *save-cache
+      - run: yarn run test-ci
+
+  test-node-6:
+    working_directory: ~/metro-bundler/packager/metro-bundler
+    docker:
+      - image: circleci/node:6
+    steps:
+      - checkout
+      - restore-cache: *restore-cache
+      - run: sudo npm i -g yarn@^1.2.1
+      - run: yarn --no-progress
+      - save-cache: *save-cache
+      - run: yarn run test-ci
+
+  deploy:
+    working_directory: ~/metro-bundler/packager/metro-bundler
+    docker:
+      - image: circleci/node:8
+    steps:
+      - checkout
+      - restore-cache: *restore-cache
+      - run:
+          working_directory: packages/metro-bundler
+          command: yarn --no-progress
+      - save-cache: *save-cache
+      - deploy: *deploy
+
+# Workflows enables us to run multiple jobs in parallel
+workflows:
+  version: 2
+  build-and-deploy:
+    jobs:
+      - test-node-9
+      - test-node-8
+      - test-node-6
+      - deploy:
+          filters:
+            branches:
+              ignore: /.*/
+            tags:
+              only: /v[0-9]+(\.[0-9]+)*/