FavourStaticEmptyFields: apply fix

Fix in FavourStaticEmptyFields rule for empty string of
fields in records.

Author: Mersho

src/FSharpLint.Core/Rules/Conventions/FavourStaticEmptyFields.fs

@@ -48,6 +48,8 @@ let private runner (args: AstNodeRuleParams) =
                 | Some(SynExpr.ArrayOrList(isArray, [], range)) ->
                     let emptyLiteralType = if isArray then EmptyArrayLiteral else EmptyListLiteral
                     generateError range emptyLiteralType
+                | Some(SynExpr.Const (SynConst.String ("", _, range), _)) ->
+                    generateError range EmptyStringLiteral
                 | _ -> Array.empty)
         |> Array.concat
     | _ -> Array.empty