fix typo in example, "multicalss" (qubvel#426)

Author: daiwt

examples/cars segmentation (camvid).ipynb

@@ -418,7 +418,7 @@
     "ENCODER = 'se_resnext50_32x4d'\n",
     "ENCODER_WEIGHTS = 'imagenet'\n",
     "CLASSES = ['car']\n",
-    "ACTIVATION = 'sigmoid' # could be None for logits or 'softmax2d' for multicalss segmentation\n",
+    "ACTIVATION = 'sigmoid' # could be None for logits or 'softmax2d' for multiclass segmentation\n",
     "DEVICE = 'cuda'\n",
     "\n",
     "# create segmentation model with pretrained encoder\n",