refactor(@angular/cli): use command default for unspecified target bu… #2192

Job	Run time
list	22s
workflow (build-unit-tests)	2m 22s
workflow (modules-builder-tests)	1m 56s
workflow (build-cli)	1m 59s
workflow (devkit-core-tests)	1m 21s
workflow (devkit-core-tests-rerun)	1m 21s
	9m 21s

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