Drop support for GHC < 8.6 #220

Job	Run time
darwin_arm (self-hosted, macOS, ARM64, 8.10.7)	1m 9s
darwin_arm (self-hosted, macOS, ARM64, 9.2.6)	58s
i386	4m 37s
arm (arm32v7)	3m 59s
build (ubuntu-latest, 8.6.5, 3.8.1.0)	5m 23s
arm (arm64v8)	3m 3s
darwin_arm (self-hosted, macOS, ARM64, 9.4.4)	1m 3s
build (ubuntu-latest, 8.8.4, 3.8.1.0)	5m 33s
build (ubuntu-latest, 8.10.7, 3.8.1.0)	5m 48s
build (ubuntu-latest, 9.0.2, 3.8.1.0)	5m 40s
build (ubuntu-latest, 9.2.8, 3.8.1.0)	3m 46s
build (ubuntu-latest, 9.4.8, 3.8.1.0)	4m 14s
build (ubuntu-latest, 9.6.3, 3.8.1.0)	2m 59s
build (ubuntu-latest, 9.8.1, 3.8.1.0)	2m 56s
build (macOS-latest, 9.4.5, 3.8.1.0)	13m 29s
build (macOS-latest, 9.6.1, 3.8.1.0)	17m 0s
build (windows-latest, 9.4.5, 3.8.1.0)	15m 22s
build (windows-latest, 9.6.1, 3.8.1.0)	16m 7s
	1h 53m 6s

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