Support `containers` version `0.8`.

[jonathanknowles]

Version 0.8 of the containers package has been released, but aeson currently has an upper bound of < 0.8:

aeson/aeson.cabal

Lines 96 to 99 in 85c2da5

	build-depends:
	, base >=4.12.0.0 && <5
	, bytestring >=0.10.8.2 && <0.13
	, containers >=0.6.0.1 && <0.8

I was able to build and test successfully with the following command:

cabal test all \
    --constraint=containers==0.8 \
    --allow-newer=hashable:containers \
    --allow-newer=indexed-traversable:containers \
    --allow-newer=scientific:containers \
    --allow-newer=semialign:containers \
    --allow-newer=witherable:containers \
    --allow-newer=quickcheck-instances:containers

Relevant upstream issues:

• Support containers version 0.8. haskellari/indexed-traversable#47
• Support containers version 0.8 (in semialign). haskellari/these#207
• Support containers version 0.8. fumieval/witherable#105
• Support containers version 0.8. haskellari/qc-instances#104
• Support containers version 0.8. haskell-unordered-containers/hashable#319
• Support containers version 0.8. basvandijk/scientific#103