Update User Agent String in Key vault with correct version and to follow azure-sdk [guidelines](https://github.com/Azure/azure-sdk/blob/74104254180ab90d56d715a14fb7b20a806ed7b8/docs/design/general/AzureCorePipeline.mdk#L20-L25).