fix(validate-commit): Update the regexp
fix(validate-commit): Update the regexp

The current regexp was sometime refusing commit messages that are
valid (see
https://travis-ci.org/algolia/instantsearch.js/builds/85530333)

I've simply removed the `?:` and added a check on the `: `, and this
seems to work better.

I still have no idea why some commits where ok and some not. If anyone
has a guess...?

algolia/instantsearch.js,algolia/react-instantsearch,algolia/react-instantsearch,algolia/instantsearch.js,algolia/react-instantsearch,algolia/react-instantsearch,algolia/instantsearch.js