Update Gemfile.lock file

I was having some issues installing gosu 0.7.48

```
In file included from ../Gosu/Gosu.hpp:19:
../Gosu/Image.hpp:117:31: warning: implicit conversion loses integer precision: 'size_type' (aka 'unsigned long') to 'int' [-Wshorten-64-to-32]
        for (int i = 0, num = tiles.size(); i < num; ++i)
                        ~~~   ^~~~~~~~~~~~
./../GosuImpl/RubyGosu_wrap.cxx:2705:9: note: in instantiation of function template specialization 'Gosu::imagesFromTiledBitmap<std::__1::vector<Gosu::Image *, std::__1::allocator<Gosu::Image *> > >' requested here
        Gosu::imagesFromTiledBitmap(window.graphics(), bmp,
        ^
63 warnings and 3 errors generated.
make: *** [RubyGosu_wrap.o] Error 1
```

I seems that is a problem related with Maverick.
Updating the gosu dependency solves the problem