Fix Docky Chrome icon

Docky no longer handles Google Chrome properly and shows two icons.  To fix it, you need to add StartupWMClass=Google-chrome-stable to each section in /usr/share/applications/google-chrome.desktop (Ubuntu and Mint, maybe be elsewhere on other distros).  You'll have to do this every time Chrome is updated.  Here's a one liner:

sudo sed -i '/^\[/a StartupWMClass=Google-chrome-stable' /usr/share/applications/google-chrome.desktop