Relax the matching of step definitions a bit

Using find() avoids the anchoring that matches() does by default. That means
the pattern is searched in the current line, instead of matched from the
start to the end.

This means that step definitions that replicate the step-keyword (some
bdd frameworks support/encourage this) or step definitions that shorten
the feature-line because some part is not necessary will also match.

In addition, at least cucumber/ruby does the matching the same way when
executing the tests and I expect other frameworks to also do non-anchored
matching.