Fixed ContentWithMoreMentionsReplaced() for roles (#521)

* Bump to v0.17.0

* Add members from GuildMembersChunk to state (#454)

* Revert "Add members from GuildMembersChunk to state (#454)" (#455)

This reverts commit e4487b30d4d846b1fdc08fd3982bd5b9965a8cc9.

* travis: update go versions

* Fixed ContentWithMoreMentionsReplaced() for roles

Discord breaking the API again? Roles seem to always be in the form `<@&id>` now

* Update message_test.go

* Removed changes

* Removed changes

Need to learn git *properly* :(