Fix latex formatting in VJP autodiff example (#1726)

Author: williambdean

doc/gallery/autodiff/vector_jacobian_product.ipynb

@@ -389,7 +389,7 @@
     "1 & 1 & 0 \\\\\n",
     "1 & 1 & 1 \\\\\n",
     "\\end{pmatrix} = \\begin{pmatrix}\n",
-    "v_1 + v2 + v 3 \\\\ v_2 + v_3 \\\\ v_3\n",
+    "v_1 + v_2 + v_3 \\\\ v_2 + v_3 \\\\ v_3\n",
     "\\end{pmatrix}\n",
     "$$"
    ]
@@ -661,7 +661,7 @@
    "source": [
     "$$\n",
     "v^T \\cdot J = \\begin{pmatrix}\n",
-    "v_1 \\\\ v_2 \\\\ v_3 \\\\ v4\n",
+    "v_1 \\\\ v_2 \\\\ v_3 \\\\ v_4\n",
     "\\end{pmatrix}^T \\cdot \\begin{pmatrix}\n",
     "x_1 & 0 \\\\\n",
     "x_2 & x_1 \\\\\n",