SQL Server URLs with instance names don't reload correctly

Stash 2.1 replaced the jTDS JDBC driver with Microsoft's own, for accessing SQL Server. Microsoft's JDBC URL allows for the following layout:

jdbc:sqlserver://hostname\instanceName:port;databaseName=database;

When using Stash's in-app screens for configuring a database, "hostname\instanceName" can be put into the hostname text box. Migration will complete successfully, and the system will connect to the desired instance.

However, when the JDBC URL is written into stash-config.properties, the \ between the hostname and instance name is not escaped (since the system does not actually support this usage). As a result, the first time the server is restarted the value becomes "hostnameinstanceName", because the \ is stripped as an invalid escape, and the database connection fails.