change version to 0.10.0.pre

the next version of pry will be 0.10.0 and to make sure plugins are
still working it's easier to drop the version requirement so that gems
like pry-debugger don't prevent pry from booting and so that pry-remote
is not a deactivated gem when pry boots.
Merge pull request #1154 from robgleeson/0.10.0-beta

change version to 0.10.0.pre