Dhall 1.23

[jneira]

• Use last dhall-to-etlas version (1.4.0.0) which uses dhall-1.23.0
• Breaking change: the empty union cases must not aplly to an empty record, so:

let defaultLang = Some (types.Languages.Haskell2010 {=})

must be

let defaultLang = Some types.Languages.Haskell2010