Fix problem loading data from default location.

[jeffhiltz]

This is my first time using github, and my first time using Ruby, so I'll start by apologizing for anything and everything, just in case. :)

I was having trouble reading data without explicitly calling set_data_file. I tracked the bug back to a recent submission. Because default_data_file_path() is in the Base singleton, 'self' already refers to the class.

This seems to have fixed it for me, hopefully it was the correct approach.

Thanks for the library.

[pushred]

This fix worked for me, thanks!

[djiang]

Works for me too! Can this please be merged into master?