Make Cancel Bounty More Explicit

[PixelantDesign]

Make Cancel Bounty a Red Button to show that it's a destructive action.

For use cases like this:

https://gitcoincommunity.slack.com/archives/C8E45J5D0/p1535973390000100

https://gitcoin.co/issue/diadata-org/api-golang/22/1027

We could also think about whether we want to allow undo of a cancelled bounty within a certain time frame.