Make the Data.Equality.Graph.Dot module compile again

[BinderDavid]

I haven't looked at whether the generated dot files are sensible, i.e. this doesn't solve #26 yet, I only took care that the module compiles again. More concretely:

• The bounds on the Graphviz dependency fixed a very ancient version of that library. I don't know whether there was a specific reason for that, but I didn't get it to compile on modern GHCs.
• Adapted the imports and the constructors to the current state of the data types.
• Added additional CI which tests that you can build the Data.Equality.Graph.Dot module

I don't know if I have enough time before our meeting to implement improved dot file generation, I have to pack tomorrow :)

[BinderDavid]

The CI build times for the Graphviz modules are with a cold cache. You can take a look at the build times in https://github.com/BinderDavid/hegg/pull/1 for how it looks like with a cache hit. Then it should be ~2min faster.

[alt-romes]

Excelent!

This is good incremental progress 👍, no hurries here!