feat(@schematics/angular): conditionally install istanbul coverage pr… #3019

Job	Run time
lint	2m 9s
build	25s
build-e2e-windows	30s
test	0s
publish-snapshots	-1s
Browser Compatibility Tests	-1s
e2e	-1s
e2e-package-managers	-1s
e2e-snapshots	-1s
e2e-windows	-1s
	2m 58s

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