title: Decimal number regular expression, where digit after decimal is optional
body: <p>I need a regular expression that validates a number, but doesn't require a digit after the decimal.
  ie.</p>
  
  <pre><code>123
  123.
  123.4
  </code></pre>
  
  <p>would all be valid</p>
  
  <pre><code>123..
  </code></pre>
  
  <p>would be invalid</p>
  
  <p>Any would be greatly appreciated!</p>