Fix repl_tester to access correct config object

Now by refactoring config, Pry.config and @pry.config have different
output. So to access correct pry config object, fix ReplTester.input
ReplTester.output and ReplTester.reset_output
Merge pull request #1110 from yui-knk/fix-repl_tester

Fix repl_tester to access correct config object