Fixes & updates

[IOAyman]

• Fixed isAfter and isBefore: The 2nd arg should be a string
• Updated documentation for isMobilePhone
• Upgraded typings tool
• Update the API to the latest version v5.6.0:
  • Added isDataURI, isMD5 validators and unescape sanitizer
• removed toString

[blakeembrey]

LGTM /cc @louy. Would you be interested in helping maintain the project? I can add you as a collaborator if you are 😄

[IOAyman]

@blakeembrey, I'd be glad to 😄

[blakeembrey]

@IOAyman Great! I've added you, just try to stick to PRs still so anyone else can jump in 😄

Edit: Also, use squashing 😄

[blakeembrey]

@IOAyman There's also the version in https://github.com/types/npm-validator/blob/master/typings.json which will usually need updating. I created some basic guidelines in https://github.com/types/guidelines, not sure how useful that is for you.

[IOAyman]

@blakeembrey, Thnaks! I'll update the remaining file, and squash things 😉