update docs to use new github user content domain
update docs to use new github user content domain

- changed raw.github.com -> raw.githubusercontent.com
- https://developer.github.com/changes/2014-04-25-user-content-security/
- pote/gpm/#30

pote/gpm,pote/gpm,jmaurice/gpm,jmaurice/gpm,foca/gpm,foca/gpm