singletons-2.7: dependencies

Dependencies for singletons-2.7

library	base (>=4.14 && <4.15) containers (>=0.5) ghc-boot-th mtl (>=2.2.1 && <2.3) pretty syb (>=0.4) template-haskell text (>=1.2) th-desugar (>=1.11 && <1.12) transformers (>=0.5.2)