Add an empty line after the badge

[dbrockman]

When GK adds the badge to a readme file it should include an empty line before and after the badge.

Without an empty line, the image will render on the same line as the text which looks weird.

[finnp]

@dbrockman Can you show an example where this is happening?

[mightyiam]

In this badge PR it did add an empty line and it is wrong. It should be smart about it.

[mightyiam]

Notice there's a fixing commit:
https://github.com/mightyiam/eslint-multiple-parsers/pull/2/commits

[chinesedfan]

In this badge PR it did add an empty line and it is wrong. It should be smart about it.

In fact, it requires readme-badger to be smarter.