Fix spec description.
Fix #run_focussed for RSpec 3.

RSpec 3 dropped support for `--line 12`. Instead `path/to/spec.rb:12` has to be used.

This commit makes RSpec 3 happy while keeping the old behaviour for RSpec 2 and older.
Merge pull request #71 from die-antwort/fix-run-focussed-for-rspec3

Fix run focussed for rspec3