Update Agda2hs

[EwenBC]

Agda-core relies on a previous version of agda2hs. Since then the commits:

• agda/agda2hs@f6bd2c8 removed Haskell.Extra.Loop
• agda/agda2hs@7f61f3d creates a conflict with the name Type
• agda/agda2hs@6c9de68 renamed agda2hs library
  (I don't know if it is an issue)

[jespercockx]

Agda Core relies on the latest released version of agda2hs, which is v1.3. So at the moment these are not issues, though they will be once the next version of agda2hs is released.