update document for load_class function

[joez]

Summary

Update document for Mojo::Loader::load_class function, because the return value is mismatch with the source code

Motivation

I am reading the Mojo source code to learn such elegant framework, and find this document mismatch with code, would like to update it if my understanding is correct

References

[kraih]

Thanks, applied.

[joez]

it's my pleasure