Fix place to specify rake-compiler version #333

Job	Run time
ruby-versions / Generate Ruby versions	3s
test (2.5, ubuntu-latest)	52s
test (2.5, macos-latest)	1m 47s
test (2.5, windows-latest)	4m 20s
test (2.6, ubuntu-latest)	54s
test (2.6, macos-latest)	1m 48s
test (2.6, windows-latest)	5m 45s
test (2.7, ubuntu-latest)	53s
test (2.7, macos-latest)	2m 54s
test (2.7, windows-latest)	4m 0s
test (3.0, ubuntu-latest)	36s
test (3.0, macos-latest)	46s
test (3.0, windows-latest)	2m 41s
test (3.1, ubuntu-latest)	37s
test (3.1, macos-latest)	48s
test (3.1, windows-latest)	3m 32s
test (3.2, ubuntu-latest)	25s
test (3.2, macos-latest)	54s
test (3.2, windows-latest)	4m 2s
test (head, ubuntu-latest)	31s
test (head, macos-latest)	51s
test (head, windows-latest)	2m 36s
test (jruby, ubuntu-latest)	6m 35s
test (jruby-head, ubuntu-latest)	6m 33s
test (truffleruby, ubuntu-latest)	4m 12s
test (truffleruby-head, ubuntu-latest)	3m 51s
	1h 2m 46s

Provide feedback