Add dependency on psych

It's not guaranteeed to be in stdlib, and Syck fucks up the
SeeingIsBelieving::Line serialization (turns it into an array)

e.g. this was causing rbx to fail
Bump version to 2.1.3

If you were on 2.1.x, the raeason minor changed rather than patch
is because the way the_matrix.rb works changed fairly significantly.
So if you overrode that file, you'll need to look at it and figure out
what to do for your thing (see #24 for an in depth explanation).

Also, added a dependency on parser. This should allow it to work on
rubinius (not tested on CI yet because some cukes are failing for
formatting reasons).