Allow ARGV to be mutated during option parsing

Reverts
f4d1f448bb
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

lib/pry/cli.rb

@@ -55,7 +55,7 @@ class Pry
         self.option_processors = nil
       end
 
-      def parse_options(args=ARGV.dup)
+      def parse_options(args=ARGV)
         unless options
           raise NoOptionsError, "No command line options defined! Use Pry::CLI.add_options to add command line options."
         end

spec/cli_spec.rb

@@ -9,6 +9,16 @@ describe Pry::Hooks do
     it 'should raise if no options defined' do
       lambda { Pry::CLI.parse_options(["--nothing"]) }.should.raise Pry::CLI::NoOptionsError
     end
+
+    it "should remove args from ARGV by default" do
+      ARGV << '-v'
+      Pry::CLI.add_options do
+        on :v, "Display the Pry version" do
+          # irrelevant
+        end
+      end.parse_options
+      ARGV.include?('-v').should == false
+    end
   end
 
   describe "adding options" do