migrates to github actions

[simonneutert]

i hope this is what you'd wanted to see, copied the key from the link you provided.

https://github.com/slack-ruby/slack-ruby-bot-server/pull/142/files

closes #42

[simonneutert]

please verify my changes for active_support I do not fully understand why rspec is having a hard time

[dblock]

Oh and add a CHANGELOG entry for this one.

[simonneutert]

I cleaned up the code @dblock

[simonneutert]

I cleaned up the code @dblock

line 14 in danger.yml errors

[simonneutert]

I hope this is working fine now, else you might need to get your hands dirty, sorry 😞

[dblock]

I merged it, will cleanup next.