udpate lts to 18.11 (#69)

src/Model.hs

@@ -6,6 +6,7 @@
 {-# LANGUAGE TemplateHaskell       #-}
 {-# LANGUAGE TypeFamilies          #-}
 {-# LANGUAGE UndecidableInstances  #-}
+{-# LANGUAGE DataKinds  #-}
 
 module Model where
 

stack.yaml

@@ -17,7 +17,7 @@
 #
 # resolver: ./custom-snapshot.yaml
 # resolver: https://example.com/snapshots/2018-01-01.yaml
-resolver: lts-16.15
+resolver: lts-18.11
 
 # User packages to be built.
 # Various formats can be used as shown in the example below.