title: Angular 5 Validators.pattern regex for only numbers
body: <p>I'm having trouble getting the Angular 5 Validators.pattern to work. I've tried every regex that SHOULD normally work, but it's not working. I read that Validators.pattern requires a different format, but I can't seem to find it...</p>
  
  <p>Any ideas what the Validators.pattern should be to</p>
  
  <p>(1) allow only numbers, positive and negative</p>
  
  <p>and </p>
  
  <p>(2) allow only numbers, positive and negative, optionally with up to 2 decimal places</p>
  
  <p>Valid examples would be: 
  1
  1.2
  1.22
  -21
  -21.48</p>
  
  <p>Anything with any letter in it would be invalid.</p>
  
  <p>Thanks for your help!</p>