Allow ARGV to be mutated during option parsing

Reverts
https://github.com/pry/pry/commit/f4d1f448bb79a8c428ad2f9c59139f831103688d
and passes ARGV rather than ARGV.dup to Pry::CLI.parse_options
by default.

@banister wasn't sure why that change was made in the first place, so
there's a wee bit of risk here. But all tests continue to pass,
and everything looks fine. If something does break, let's make sure
to add tests for it this time around! <3 <3 <3

Resolves https://github.com/pry/pry/issues/968, where
the '-r' argument was being passed through and throwing an error
when the file being required began with #puts
Merge pull request #969 from DanielleSucher/fix-issue-968

Allow ARGV to be mutated during option parsing