Including missing field name in short error message (#1519)

* Including missing field name in short error message

Fixes #1513

* Escape reserved labels in the error message

... as suggested by @sjakobi

Author: Gabriella439

dhall/src/Dhall/TypeCheck.hs

@@ -3687,7 +3687,7 @@ prettyTypeMessage (CantProjectByExpression expr) = ErrorMessages {..}
 
 prettyTypeMessage (MissingField k expr0) = ErrorMessages {..}
   where
-    short = "Missing record field"
+    short = "Missing record field: " <> Dhall.Pretty.Internal.prettyLabel k
 
     long =
         "Explanation: You can only access fields on records, like this:                  \n\