Reminder: Check links in print.html again

[adamgreen]

Revert commit bb36fd6 once rust-lang/mdBook#789 is fixed so that mdBook properly handles relative links in print.html

[therealprof]

@adamgreen any idea why it started failing again? cf. https://travis-ci.org/rust-embedded/bookshelf/builds

[adamgreen]

@therealprof After commit rust-embedded/book@cf66108 the main rust book is failing too. I am preparing a PR for this now. I should have it ready in a few minutes.

[adamgreen]

@therealprof PR #12 should fix this issue.