Create directory on output

[iMobs]

PR checklist

• Addresses an existing issue: Closes Create directory on output #4268
• New feature, bugfix, or enhancement
  • Includes tests
• Documentation update

Overview of change:

Use mkdirp to create output directory if necessary to avoid ENOENT error when output path does not exist.

CHANGELOG.md entry:

[bugfix] Create output directory when the output path (specified by --out CLI flag) does not exist.

[palantirtech]

Thanks for your interest in palantir/tslint, @iMobs! Before we can accept your pull request, you need to sign our contributor license agreement - just visit https://cla.palantir.com/ and follow the instructions. Once you sign, I'll automatically update this pull request.

[adidahiya]

thanks @iMobs