add dependency to gemspec

when I type

```bundle exec qlang -i```

then

```
/Users/taish/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/qlang-0.0.27180000/lib/qlang/lexer/wrap_lexer.rb:1:in `require': cannot load such file -- pry (LoadError)
```
So I added dependency to gemspec .

But I didn't see your code.
Maybe you might write a wrong for debug lol
If so, Please close