update drush version

env-example

@@ -88,7 +88,7 @@ WORKSPACE_INSTALL_MONGO=false
 WORKSPACE_INSTALL_AMQP=false
 WORKSPACE_INSTALL_MSSQL=false
 WORKSPACE_INSTALL_DRUSH=false
-WORKSPACE_DRUSH_VERSION=8.1.16
+WORKSPACE_DRUSH_VERSION=8.1.17
 WORKSPACE_INSTALL_DRUPAL_CONSOLE=false
 WORKSPACE_INSTALL_AEROSPIKE=false
 WORKSPACE_INSTALL_V8JS=false