It's a typo. The documentation is like all documentation -- don't trust it further than you can throw it. Just because the documentation suggests one way of doing it doesn't mean you aren't allowed to use good sense and improve it.

Please use a semi-colon and put this line in a BEGIN block. Also, I'd prefer this to be entirely isolated to the `DW::OAuth` module, so that we don't have to clutter up other modules by including both. (If you include `Net::OAuth` in the `DW::OAuth` module, it will be imported into the namespace and able to be called from anybody who imports `DW::OAuth`.)