* Implemented a version check of npm to give a soft tip during the install procedure
and fixed gitignore
* Moved NPM check to method, it is only executed when you use NPM and the version is < 3.
* Minor formatting tweaks
* Simplify the code
* Remove unnecessary change
The Contributing instructions in the README give my-app as the sample
app name when running `npm run create-react-app my-app`. This just adds
those directories to the .gitignore so they don't accidentally get
committed.
Test Plan:
```
npm pack
node global-cli/index.js testing --scripts-version /Users/vjeux/random/react-getting-started/create-react-app-scripts-0.0.1.tgz
```
make sure it shows
```
Creating the app testing at /Users/vjeux/random/react-getting-started/testing
```