fixup! fixup! fixup! Various Thunk->DTask renames

Author: jpsamaroo

Diff for: test/thunk.jl

@@ -179,7 +179,7 @@ end
             ex_str = sprint(io->Base.showerror(io,ex))
             @test occursin(r"^DTaskFailedException:", ex_str)
             @test occursin("Test", ex_str)
-            @test !occursin("Root Thunk", ex_str)
+            @test !occursin("Root Task", ex_str)
 
             ex = try
                 fetch(b)
@@ -189,7 +189,7 @@ end
             ex = Dagger.Sch.unwrap_nested_exception(ex)
             ex_str = sprint(io->Base.showerror(io,ex))
             @test occursin("Test", ex_str)
-            @test occursin("Root Thunk", ex_str)
+            @test occursin("Root Task", ex_str)
         end
         @testset "single dependent" begin
             a = @spawn error("Test")