title: Ruby Regexp gsub, replace instances of second matching character
body: <p>I would like to replace the first letter after a hyphen in a string with a capitalised letter.</p>
  
  <p>"this-is-a-string" should become "thisIsAString"</p>
  
  <pre><code>"this-is-a-string".gsub( /[-]\w/, '\1'.upcase ) 
  </code></pre>
  
  <p>I was hoping that \1 would reinsert my second character match  \w and that I could capitalise it.</p>
  
  <p>How does one use the \0 \1 etc options?</p>