Update Azure button to deploy from master

Author: toolboc

articles/iot-edge/how-to-install-iot-edge-ubuntuvm.md

@@ -29,7 +29,7 @@ The [Deploy to Azure Button](../azure-resource-manager/templates/deploy-to-azure
 
 1. We will deploy an Azure IoT Edge enabled Linux VM using the iotedge-vm-deploy ARM Template.  To begin, click the button below:
 
-    [![Deploy to Azure Button for iotedge-vm-deploy](https://aka.ms/deploytoazurebutton)](https://portal.azure.com/#create/Microsoft.Template/uri/https%3A%2F%2Fraw.githubusercontent.com%2Fazure%2Fiotedge-vm-deploy%2Fms-learn%2FedgeDeploy.json)
+    [![Deploy to Azure Button for iotedge-vm-deploy](https://aka.ms/deploytoazurebutton)](https://portal.azure.com/#create/Microsoft.Template/uri/https%3A%2F%2Fraw.githubusercontent.com%2Fazure%2Fiotedge-vm-deploy%2Fmaster%2FedgeDeploy.json)
 
 1. On the newly launched window, fill in the available form fields: