Update bootstrap.properties (#969)

examples/QuickStart/JavaSpring/QuickStart/src/main/resources/bootstrap.properties

@@ -1,4 +1,4 @@
 spring.application.name=QuickStart
 # Either a connection string or endpoint needs to be provided per store.
 # All possible configurations can be found in the [README](https://github.com/Azure/azure-sdk-for-java/tree/main/sdk/spring/spring-cloud-azure-starter-appconfiguration-config)
-spring.cloud.azure.appconfiguration.stores[0].connection-string= ${APP_CONFIGURATION_CONNECTION_STRING}
+spring.cloud.azure.appconfiguration.stores[0].connection-string= ${AZURE_APPCONFIG_CONNECTION_STRING}