Exclude vendor and other directories when generating rdoc

[wildmaples]

Exclude:

• Gemfile
• Rakefile
• "vendor/*"
• "bin/*"
• "test/*"

We initially only talked about the vendor directory. However, I made the decision to add the rest of the directories because they didn't contain any documentation (and so was formatted poorly) and cluttered up the side bar.

Tested on my fork