change incorrect instruction

Both backwards and forward passes need to be done by the student.

first-neural-network/Your_first_neural_network.ipynb

@@ -190,7 +190,7 @@
    "source": [
     "## Time to build the network\n",
     "\n",
-    "Below you'll build your network. We've built out the structure and the backwards pass. You'll implement the forward pass through the network. You'll also set the hyperparameters: the learning rate, the number of hidden units, and the number of training passes.\n",
+    "Below you'll build your network. We've built out the structure. You'll implement both the forward pass and backwards pass through the network. You'll also set the hyperparameters: the learning rate, the number of hidden units, and the number of training passes.\n",
     "\n",
     "<img src=\"assets/neural_network.png\" width=300px>\n",
     "\n",