updated heading of Canonical forms

Author: tclose

docs/source/tutorial/7-canonical-form.ipynb

@@ -4,7 +4,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "# Canonical form and serialisation\n",
+    "# Canonical forms\n",
     "\n",
     "## Canonical task form\n",
     "\n",