src/ehc: port to hashable-1.2

'combine' is gone away, but hashWithSalt is a drop-in replacement.

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
local changes
merge of fixes for hashable-1.2
Merge branch 'master' of github.com:UU-ComputerScience/uhc into polyvariant-strictness