Fixed whitespace rule for trivial for cases.

[WiseBird]

PR checklist

• Addresses an existing issue: Bug with whitespace #2382
• New feature, bugfix, or enhancement
  • Includes tests
• Documentation update

Overview of change:

whitespace rule no longer reports for statement with one part missing as an error, e.g.:

    for (x = 2; x--;) {}
    for (;;) {}

[palantirtech]

Thanks for your interest in palantir/tslint, @WiseBird! 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.

[ajafff]

Thanks @WiseBird