fixing usinc typo

tutorials/image/cifar10_estimator/README.md

@@ -41,7 +41,7 @@ $ python cifar10_main.py --data_dir=/prefix/to/downloaded/data/cifar-10-batches-
                          --num_gpus=2 \
                          --train_steps=1000
 
-# Run the model on 2 GPUs usinc GPU as parameter server. After training, it runs the evaluation.
+# Run the model on 2 GPUs using GPU as parameter server. After training, it runs the evaluation.
 $ python cifar10_main.py --data_dir=/prefix/to/downloaded/data/cifar-10-batches-bin \
                          --model_dir=/tmp/cifar10 \
                          --is_cpu_ps=False \