Dropping containers support for old GHC versions

[Henning Thielemann]

On Fri, 9 Mar 2018, Daniel Cartwright wrote:

> I am +1 on this.
> GHC 7.0 is 8 years old
> GHC 7.2 is 7 years old
> GHC 7.4 is 6 years old
> 
> On a related note, I find it strange when looking through source code for 'containers'/other Haskell libraries
> and still see notes about supporting non-GHC Haskell compilers (e.g. Hugs)

Recently we got to install Hugs on a Lego machine - installation required 
several minutes. I would not try to install GHC there.