removed single-quotes from logback.xml template

[davidkron]

It seems the single-quotes were copied from logback.groovy, but they are not necessary.

Before this change, the single-quotes were printed to the console, which looked weird:

'2022-01-26 14:40:38.140  WARN --- [  restartedMain] org.grails.config.NavigableMap           : Accessing config key '[plugins]' through dot notation is deprecated, and it will be removed in a future release. Use 'config.getProperty(key, targetClass)' instead.
''2022-01-26 14:40:43.486  WARN --- [  restartedMain] org.grails.config.NavigableMap           : Accessing config key '[plugins, springsecurity]' through dot notation is deprecated, and it will be removed in a future release. Use 'config.getProperty(key, targetClass)' instead.
'