Use bundle exec #148

Job	Run time
ruby-versions / Generate Ruby versions	4s
build (2.5 / ubuntu-latest)	29s
build (2.5 / macos-latest)	51s
build (2.5 / windows-latest)	3m 32s
build (2.6 / ubuntu-latest)	23s
build (2.6 / macos-latest)	1m 3s
build (2.6 / windows-latest)	3m 27s
build (2.7 / ubuntu-latest)	28s
build (2.7 / macos-latest)	55s
build (2.7 / windows-latest)	2m 8s
build (3.0 / ubuntu-latest)	12s
build (3.0 / macos-latest)	16s
build (3.0 / windows-latest)	1m 34s
build (3.1 / ubuntu-latest)	13s
build (3.1 / macos-latest)	16s
build (3.1 / windows-latest)	1m 45s
build (3.2 / ubuntu-latest)	9s
build (3.2 / macos-latest)	34s
build (3.2 / windows-latest)	2m 38s
build (head / ubuntu-latest)	10s
build (head / macos-latest)	15s
build (jruby / ubuntu-latest)	59s
build (jruby-head / ubuntu-latest)	1m 9s
build (truffleruby / ubuntu-latest)	38s
build (truffleruby / macos-latest)	1m 14s
build (truffleruby-head / ubuntu-latest)	36s
build (truffleruby-head / macos-latest)	1m 20s
build (mingw / windows-latest)	1m 23s
build (mswin / windows-latest)	1m 51s
	30m 32s

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