Test only - update sqlserver test docker image to 2017-CU31-ubuntu-18.04

Author: rbygrave

ebean-test/testconfig/ebean-sqlserver17.properties

@@ -1,6 +1,6 @@
 ebean.test.platform=sqlserver
 ebean.test.dbName=test_ebean
-ebean.test.sqlserver.version=2017-CU28-ubuntu-16.04
+ebean.test.sqlserver.version=2017-CU31-ubuntu-18.04
 ebean.test.sqlserver.containerName=local_sqlserver2017
 ebean.test.sqlserver.collation=LATIN1_GENERAL_100_CS_AS_SC
 ebean.test.sqlserver.port=9435