singletons-2.6: dependencies

Dependencies for singletons-2.6

library	base (>=4.13 && <4.14) containers (>=0.5) ghc-boot-th mtl (>=2.2.1 && <2.3) pretty syb (>=0.4) template-haskell text (>=1.2) th-desugar (>=1.10 && <1.11) transformers (>=0.5.2)