Minor RSI tweaks

Just bringing it in line with the SVG structure of the other series, having a single 'g' element as  the parent for all series elements.

<g class="rsi">
  <line .../>
  <line .../>
  <line .../>
  <path .../>
</g>
Merge pull request #163 from ColinEberhardt/rsi-update

Minor RSI tweaks