Fix very minor misspelling in Quantity tutorial

Author: eteq

tutorials/Quantities/Quantities.ipynb

@@ -359,7 +359,7 @@
      "cell_type": "markdown",
      "metadata": {},
      "source": [
-      "However, you can't take the log of something with units, as that is not mathmatically sensible."
+      "However, you can't take the log of something with units, as that is not mathematically sensible."
      ]
     },
     {
@@ -977,4 +977,4 @@
    "metadata": {}
   }
  ]
-}
+}