modified comment for image augmentation line import to include correct 'pip3...

modified comment for image augmentation line import to include correct 'pip3 install imgaug' instructions

samples/coco/coco.py

@@ -31,7 +31,7 @@ import os
 import sys
 import time
 import numpy as np
-import imgaug  # https://github.com/aleju/imgaug (pip3 install imageaug)
+import imgaug  # https://github.com/aleju/imgaug (pip3 install imgaug)
 
 # Download and install the Python COCO tools from https://github.com/waleedka/coco
 # That's a fork from the original https://github.com/pdollar/coco with a bug