title: stringr package str_extract() with inversion of the regex
body: <p>I have a string like the following: 
  14ed0d69fa2.bbd.7f5512.filter-132.21026.55B67C8E27.0</p>
  
  <p>The following regex extracts the last part that ends in a dot and a digit. I want to extract everything but that part and can't seem to find a way to invert the regex (using ^) is not helping:</p>
  
  <pre><code>&gt; s &lt;- '14ed0d69fa2.bbd.7f5512.filter-132.21026.55B67C8E27.0'
  &gt; str_extract(s, '(\\.[0-9]{1})$')
  [1] ".0"
  </code></pre>
  
  <p>I instead want the output to be:</p>
  
  <pre><code>[1] 14ed0d69fa2.bbd.7f5512.filter-132.21026.55B67C8E27
  </code></pre>
  
  <p>To clarify further, I want it to return the string as is, if it does not end in a dot and one single digit.</p>
  
  <p>Following example:</p>
  
  <pre><code>&gt; s &lt;- '14ed0d69fa2.bbd.7f5512.filter-132.21026.55B67C8E27'
  &gt; str_extract(s, someRegex)
  [1] "14ed0d69fa2.bbd.7f5512.filter-132.21026.55B67C8E27"
  &gt; s &lt;- '14ed0d69fa2.bbd.7f5512.filter-132.21026.55B67C8E27.1'
  &gt; str_extract(s, someRegex)
  [1] "14ed0d69fa2.bbd.7f5512.filter-132.21026.55B67C8E27"
  &gt; s &lt;- '14ed0d69fa2.bbd.7f5512.filter-132.21026.55B67C8E27.4'
  &gt; str_extract(s, someRegex)
  [1] "14ed0d69fa2.bbd.7f5512.filter-132.21026.55B67C8E27"
  </code></pre>