CI on travis missing testing for ghc 8.2 - 8.10

[andreasabel]

Seems like only GHC versions up to 8.0 are tested:

Shelly.hs/.travis.yml

Lines 5 to 10 in 1b6643a

	env:
	- CABALVER=1.18 GHCVER=7.6.3
	- CABALVER=1.18 GHCVER=7.8.4
	- CABALVER=1.22 GHCVER=7.10.2
	- CABALVER=1.24 GHCVER=8.0.1
	- CABALVER=2.0 GHCVER=8.0.2