locked to purescript 0.7

[hedefalk]

Seemed that 0.10.2 of PS (psc) which I have globally didn't support ffi param pulp sent:

* Invalid option `--ffi=src/**/*.js'

So I tried updating pulp, but then there were other errors instead:

> pulp dep install
* Error: Unknown command: "dep"

> pulp server --no-info

* Error: Unrecognised arguments: --no-info

plus compile errors from updating PS.

So maybe just lock PS version and clone + do what README says works…?