in CI, don't specify full scala version #933

Job	Run time
Compile Benchmarks	1m 4s
Docs	2m 20s
Checks	1m 34s
Compile and test (2.12, 8)	3m 48s
Compile and test (2.12, 11)	3m 42s
Gradle tests	2m 57s
Maven tests	2m 32s
sbt scripted tests (gen-scala-server, 2.12)	8m 8s
sbt scripted tests (gen-java, 2.12)	3m 37s
Compile and test (2.12, 17)	3m 53s
Compile and test (2.12, 21)	3m 57s
Compile and test (2.13, 8)	4m 18s
Compile and test (2.13, 11)	4m 1s
Compile and test (2.13, 17)	4m 16s
Compile and test (2.13, 21)	3m 50s
Compile and test (3.3, 8)	4m 22s
Compile and test (3.3, 11)	4m 19s
Compile and test (3.3, 17)	4m 19s
Compile and test (3.3, 21)	3m 56s
	1h 10m 53s

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