Refer to the library name instead of the constant

When we are loading a component and we want to know its version, we are
actually not speaking about the constant but the library itself.

[ci skip]

[Godfrey Chan & Xavier Noria]
After rack 1.6.0, by default, the rack will also out put the log which is not intent in rails.

Such change will also close the quiet_assets [#36](https://github.com/evrone/quiet_assets/issues/36) issue.