Update train-model.md

Author: aahill

articles/cognitive-services/language-service/custom-classification/how-to/train-model.md

@@ -30,7 +30,7 @@ See the [application development lifecycle](../overview.md#project-development-l
 
 ## Data split
 
-Before starting the training process, files in your dataset are divided into three groups at random:
+Before you start the training process, files in your dataset are divided into three groups at random:
 
 * The **training set** contains 80% of the files in your dataset. It is the main set that is used to train the model.