fix 1.6

Author: mcabbott

src/functor.jl

@@ -154,7 +154,7 @@ if VERSION < v"1.7"
   # Copied verbatim from Base, except omitting the macro:
   function ismutabletype(@nospecialize t)
       # @_total_meta  
-      t = unwrap_unionall(t)
+      t = Base.unwrap_unionall(t)
       return isa(t, DataType) && t.name.flags & 0x2 == 0x2
   end
 end