Minor fix in type hint and stringdoc

*predict_next_note* currently says it returns an ID, where the return type is int, but it actually returns a tuple.

Author: felipetovarhenao

site/en/tutorials/audio/music_generation.ipynb

@@ -1073,8 +1073,8 @@
         "def predict_next_note(\n",
         "    notes: np.ndarray, \n",
         "    keras_model: tf.keras.Model, \n",
-        "    temperature: float = 1.0) -> int:\n",
-        "  \"\"\"Generates a note IDs using a trained sequence model.\"\"\"\n",
+        "    temperature: float = 1.0) -> Tuple:\n",
+        "  \"\"\"Generates a note as a tuple of (pitch, step, duration), using a trained sequence model.\"\"\"\n",
         "\n",
         "  assert temperature > 0\n",
         "\n",