Conflict with `hashable==1.2.5.0`: Ambiguous occurrence for `Hashed' and `unhashed'

Unsure if this is something to be fixed in this package or the [`hashable`](https://github.com/tibbe/hashable) package, but thought it was worth posting at the very least to spread awareness.

```
$ cabal install --constraint 'transformers installed' lambdabot-5.1 djinn
…
Building hashable-extras-0.2.3...
Failed to install hashable-extras-0.2.3
Build log ( /root/.cabal/logs/hashable-extras-0.2.3.log ):
cabal: Entering directory '/tmp/cabal-tmp-10/hashable-extras-0.2.3'
[1 of 1] Compiling Main ( /tmp/cabal-tmp-10/hashable-extras-0.2.3/dist/setup/setup.hs, /tmp/cabal-tmp-10/hashable-extras-0.2.3/dist/setup/Main.o )
Linking /tmp/cabal-tmp-10/hashable-extras-0.2.3/dist/setup/setup ...
Configuring hashable-extras-0.2.3...
Building hashable-extras-0.2.3...
Preprocessing library hashable-extras-0.2.3...
[1 of 1] Compiling Data.Hashable.Extras ( src/Data/Hashable/Extras.hs, dist/build/Data/Hashable/Extras.o )

src/Data/Hashable/Extras.hs:30:19: error:
Ambiguous occurrence `Hashed'
It could refer to either `Data.Hashable.Hashed',
imported from `Data.Hashable' at src/Data/Hashable/Extras.hs:26:1-20
(and originally defined in `hashable-1.2.5.0:Data.Hashable.Class')
or `Data.Hashable.Extras.Hashed',
defined at src/Data/Hashable/Extras.hs:28:1

src/Data/Hashable/Extras.hs:31:22: error:
Ambiguous occurrence `unhashed'
It could refer to either `Data.Hashable.unhashed',
imported from `Data.Hashable' at src/Data/Hashable/Extras.hs:26:1-20
(and originally defined in `hashable-1.2.5.0:Data.Hashable.Class')
or `Data.Hashable.Extras.unhashed',
defined at src/Data/Hashable/Extras.hs:28:24
cabal: Leaving directory '/tmp/cabal-tmp-10/hashable-extras-0.2.3'
…
cabal: Error: some packages failed to install:
dice-0.1 depends on hashable-extras-0.2.3 which failed to install.
hashable-extras-0.2.3 failed during the building phase. The exception was:
ExitFailure 1
lambdabot-5.1 depends on hashable-extras-0.2.3 which failed to install.
…
```

----

Adding `--constraint=hashable==1.2.4.0` to the `cabal install` gets around the issue.