haddock: Fix submodule commit to point to ghc-head
haddock: Fix submodule commit to point to ghc-head

6746549772c5 accidentally pointed it to a branch (wip/rae-nokinds), before
rebasing it onto ghc-head.

Signed-off-by: Austin Seipp <7ea35d812706d9213868749011af1ed4fa2f6aa0@well-typed.com>

oldmanmike/ghc,sgillespie/ghc,tjakway/ghcjvm,GaloisInc/halvm-ghc,snoyberg/ghc,mettekou/ghc,nushio3/ghc,mcschroeder/ghc,olsner/ghc,gridaphobe/ghc,mcschroeder/ghc,mettekou/ghc,nushio3/ghc,mettekou/ghc,ezyang/ghc,gridaphobe/ghc,mettekou/ghc,nushio3/ghc,oldmanmike/ghc,shlevy/ghc,ezyang/ghc,mcschroeder/ghc,olsner/ghc,gridaphobe/ghc,vikraman/ghc,oldmanmike/ghc,GaloisInc/halvm-ghc,tjakway/ghcjvm,sgillespie/ghc,snoyberg/ghc,vikraman/ghc,shlevy/ghc,GaloisInc/halvm-ghc,ezyang/ghc,vikraman/ghc,shlevy/ghc,snoyberg/ghc,sgillespie/ghc,mcschroeder/ghc,vTurbine/ghc,olsner/ghc,mcschroeder/ghc,shlevy/ghc,mettekou/ghc,vikraman/ghc,tjakway/ghcjvm,vikraman/ghc,GaloisInc/halvm-ghc,nushio3/ghc,nushio3/ghc,olsner/ghc,snoyberg/ghc,oldmanmike/ghc,vTurbine/ghc,gridaphobe/ghc,sdiehl/ghc,GaloisInc/halvm-ghc,vTurbine/ghc,GaloisInc/halvm-ghc,snoyberg/ghc,sgillespie/ghc,olsner/ghc,vTurbine/ghc,ezyang/ghc,mcschroeder/ghc,vTurbine/ghc,shlevy/ghc,sdiehl/ghc,sdiehl/ghc,tjakway/ghcjvm,gridaphobe/ghc,sdiehl/ghc,ezyang/ghc,vTurbine/ghc,snoyberg/ghc,sgillespie/ghc,sdiehl/ghc,oldmanmike/ghc,tjakway/ghcjvm,gridaphobe/ghc,shlevy/ghc,sdiehl/ghc,mettekou/ghc,mettekou/ghc,gridaphobe/ghc,oldmanmike/ghc,snoyberg/ghc,vikraman/ghc,oldmanmike/ghc,mcschroeder/ghc,sdiehl/ghc,ezyang/ghc,tjakway/ghcjvm,nushio3/ghc,olsner/ghc,nushio3/ghc,ezyang/ghc,GaloisInc/halvm-ghc,tjakway/ghcjvm,vTurbine/ghc,sgillespie/ghc,shlevy/ghc,sgillespie/ghc,vikraman/ghc,olsner/ghc