Update 12_2_Multihead_Self_Attention.ipynb

title number is incorrect, its actually 12.2

Notebooks/Chap12/12_2_Multihead_Self_Attention.ipynb

@@ -28,7 +28,7 @@
     {
       "cell_type": "markdown",
       "source": [
-        "# **Notebook 12.1: Multihead Self-Attention**\n",
+        "# **Notebook 12.2: Multihead Self-Attention**\n",
         "\n",
         "This notebook builds a multihead self-attention mechanism as in figure 12.6\n",
         "\n",