Loofah::HTML5::WhiteList is deprecated

[vividtone]

A warning message "constant Loofah::HTML5::WhiteList is deprecated" is shown if you update Loofah to 2.3.0.

In Loofah 2.3.0, Loofah::HTML5::WhiteList was renamed to Loofah::HTML5::SafeList.
flavorjones/loofah#164

[bary822]

I guess this should be fixed in the newest version?
#100

[vividtone]

I guess this should be fixed in the newest version?
#100

@bary822 Oh, I overlooked the pull request. Thank you for pointing it out.