Add source-repository to .cabal file. Also, added upper bound to base constraint.
Add source-repository to .cabal file. Also, added upper bound to base constraint.

laszlopandy/elm-compiler,5outh/Elm,pairyo/elm-compiler,JoeyEremondi/elm-pattern-effects,deadfoxygrandpa/Elm,Axure/elm-compiler,mgold/Elm