Update what-are-parallel-documents.md

removed en-us from URL

Author: melghazali

articles/cognitive-services/Translator/custom-translator/what-are-parallel-documents.md

@@ -23,7 +23,7 @@ system in either direction.
 
 ## Requirements
 
-You will need a minimum of 10,000 unique aligned parallel sentences to train a system. This limitation is a safety net to ensure your parallel sentences contain enough unique vocabulary to successfully train a translation model. As a best practice, continuously add more parallel content and retrain to improve the quality of your translation system. Please refer to [Sentence Alignment](https://docs.microsoft.com/en-us/azure/cognitive-services/translator/custom-translator/sentence-alignment).
+You will need a minimum of 10,000 unique aligned parallel sentences to train a system. This limitation is a safety net to ensure your parallel sentences contain enough unique vocabulary to successfully train a translation model. As a best practice, continuously add more parallel content and retrain to improve the quality of your translation system. Please refer to [Sentence Alignment](https://docs.microsoft.com/azure/cognitive-services/translator/custom-translator/sentence-alignment).
 
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