CircleCI is faster and has more features than Travis CI. Additionally,
based on the recent news, the future of Travis CI is rather uncertain.
Keep using Travis CI for macOS testing at the moment, as open source
projects will need to get special permission to use CircleCI for macOS
tests.
Support for channels is not complete. The following pieces are missing:
* Channels with values bigger than int. An int in TinyGo can always
contain at least a pointer, so pointers are okay to send.
* Buffered channels.
* The select statement.
