Correcting typo (#341)

Typo in header, assuming it should be using instead of usubg

Author: brendonotto

articles/bot-service-build-download-source-code.md

@@ -54,7 +54,7 @@ After your project configured, your project changes will be published to Azure.
 
 Next, we'll take a look at downloading and redeploying code using the `az` cli.
 
-### Download code usubg Azure CLI
+### Download code using Azure CLI
 First, log in to the Azure portal using the az cli tool.
 
 ```azcli