Allowing pry 0.10.x

Since `pry` has updated, this change to the version range will allow `pry-nav` to be around in a set of gems when `pry` 0.10.x is used.

My work requires me to continue supporting Ruby 1.8.7 (:grimacing:), so I make use of `pry-nav` instead of some of the newer, neater tools you've made @nixme.

I've done some basic testing locally and things seem functional with the new version of `pry`. Is there further specific checking you'd want done to clear the way for this change?