bug: cargo doesn't know how to resolve dependencies for print-rcdom

[coolaj86]

See #476

If you use "*" for the dependency version, cargo cannot resolve the versions correctly:

[dependencies]
html5ever = "*"
markup5ever_rcdom = "*"

Fix: use exact dependencies

[dependencies]
html5ever = "0.25.2"
markup5ever_rcdom = "0.1.0"

Not sure if this is a bug in how the versions have been published, or a bug in cargo itself.

[coolaj86]

Recording of me walking through this, step-by-step, verbatim and demonstrating the bug:

Starts at timestamp 2:30:05: https://youtu.be/xu2r8tuUs6k?t=9005

Exact bug discovered at 2:38:15: https://youtu.be/xu2r8tuUs6k?t=9495