test

Reenable Travis CI. #194

Job	Run time
ruby-versions / Generate Ruby versions	4s
build (2.5 / ubuntu-latest)	23s
build (2.5 / windows-latest)	3m 18s
build (2.6 / ubuntu-latest)	26s
build (2.6 / macos-latest)	45s
build (2.6 / windows-latest)	3m 4s
build (2.7 / ubuntu-latest)	27s
build (2.7 / macos-latest)	48s
build (2.7 / windows-latest)	2m 38s
build (3.0 / ubuntu-latest)	13s
build (3.0 / macos-latest)	18s
build (3.0 / windows-latest)	1m 46s
build (3.1 / ubuntu-latest)	14s
build (3.1 / macos-latest)	21s
build (3.1 / windows-latest)	1m 29s
build (3.2 / ubuntu-latest)	13s
build (3.2 / macos-latest)	13s
build (3.2 / windows-latest)	1m 50s
build (3.3 / ubuntu-latest)	11s
build (3.3 / macos-latest)	17s
build (3.3 / windows-latest)	2m 51s
build (head / ubuntu-latest)	10s
build (head / macos-latest)	17s
build (truffleruby-head / ubuntu-latest)	30s
build (truffleruby-head / macos-latest)	47s
build (mswin / windows-latest)	1m 50s
build (mingw / windows-latest)	1m 36s
	26m 59s

Provide feedback