poudriere: http://space.kvedulv.de/FreeBSD/ruby21-gems-2.4.8.log
portlint:
```
mmoll@marduk:/usr/ports/devel/ruby-gems$ portlint -ACNc
WARN: Makefile: [10]: possible direct use of command "ruby" found. use ${RUBY} instead.
0 fatal errors and 1 warning found.
```