docs: tweak one example from the batches where the classic API is used, just in case someone copies it to use in other contexts.

Author: PMeira

docs/examples/Batches.ipynb

@@ -621,6 +621,7 @@
    "source": [
     "%%timeit\n",
     "power_spec_classic_prop = np.zeros(dss.ActiveCircuit.Loads.Count, dtype=complex)\n",
+    "dss.ActiveCircuit.SetActiveClass('Load')\n",
     "idx = dss.ActiveCircuit.Loads.First\n",
     "while idx != 0:\n",
     "    dss.Text.Command = '? kW'\n",