title: Replace uppercase with lowercase letters
body: <p>I'm trying to replace uppercase letters with corresponding lowercase letters using regex.
  So that</p>
  
  <pre><code>EarTH:   1,
  MerCury: 0.2408467,
  venuS:   0.61519726,
  </code></pre>
  
  <p>becomes</p>
  
  <pre><code>earth:   1,
  mercury: 0.2408467,
  venus:   0.61519726,
  </code></pre>
  
  <p>in Sublime Text. How can I downcase letters only in words that contain both lower and uppercase letters? So that it affects <code>venUs</code> and not <code>VENUS</code>.</p>