Update one missing word in explanation

intro-to-pytorch/Part 3 - Training Neural Networks (Exercises).ipynb

@@ -427,7 +427,7 @@
    "source": [
     "### Training for real\n",
     "\n",
-    "Now we'll put this algorithm into a loop so we can go through all the images. Some nomenclature, one pass through the entire dataset is called an *epoch*. So here we're going to loop through `trainloader` to get our training batches. For each batch, we'll doing a training pass where we calculate the loss, do a backwards pass, and update the weights.\n",
+    "Now we'll put this algorithm into a loop so we can go through all the images. Some nomenclature, one pass through the entire dataset is called an *epoch*. So here we're going to loop through `trainloader` to get our training batches. For each batch, we'll be doing a training pass where we calculate the loss, do a backwards pass, and update the weights.\n",
     "\n",
     ">**Exercise:** Implement the training pass for our network. If you implemented it correctly, you should see the training loss drop with each epoch."
    ]