shortdef adds redundant block

[ngphuoc]

julia> ex = :(f(x,y) = x+y) |> striplines;

julia> for i=1:10
         global ex = @> ex longdef shortdef
         end

julia> ex
:(f(x, y) = begin
          begin
              begin
                  begin
                      begin
                          begin
                              begin
                                  begin
                                      begin
                                          begin
                                              begin
                                                  x + y
                                              end
                                          end
                                      end
                                  end
                              end
                          end
                      end
                  end
              end
          end
      end)

[cstjean]

This was fixed by #100, although we're still missing a test case.