Auto merge of #5479 - myersjustinc:man-source-refs, r=segiddins
Auto merge of #5479 - myersjustinc:man-source-refs, r=segiddins

Update `Gemfile` docs' link targets for `:source`

These two links don't go anywhere in the browser, most likely because 01fc34bebd128d758733261f16d9e9a8523d81d4 changed the text of those (and other) headers.

As far as I know (based on a quick search with `/\w+-)/`), these are the only two links with this problem.

bundler/bundler,mvz/bundler,mvz/bundler,dilumnavanjana/bundler,bundler/bundler,dilumnavanjana/bundler