github urls trigger warning

[owocki]

itd be cool if slack protector didnt post warnings when a github URL is put into channel

example case here => http://bits.owocki.com/3k021q2V0n3e/Image%202017-10-21%20at%201.20.00%20PM.png

[mateodelnorte]

can make a fix here, but we're pretty much moving over to coz-slack-ico-management-platform for our bot. best to combine efforts. 😄