v1.3.0

• Deprecated many node versions, only currently support (https://www.pivotaltracker.com/story/show/90697200)
  • 0.8.27
  • 0.8.28
  • 0.9.11
  • 0.9.12
  • 0.10.37
  • 0.10.38
  • 0.11.15
  • 0.11.16
  • 0.12.1
  • 0.12.2
• Document Contribution guidelines (https://www.pivotaltracker.com/story/show/92459188)
• Added cache-busting for stack switching (https://www.pivotaltracker.com/story/show/91630606)
• Merge upstream changes from Heroku up to SHA 40214da (https://www.pivotaltracker.com/story/show/90537740