Update bundler v1.6 rationale doc, and some minor fixes.

- [x] Add a anchor for jumping to summary.
- [x] Update gem version in example more close to recent versions.
- [x] Update http://rubygems.org to https.
Merge pull request #116 from JuanitoFatas/patch/update-rationale-of-16

Update bundler v1.6 rationale doc, and some minor updates.