Support Gradle 6.2 (due to changes in org.gradle.util.SingleMessageLogger)

[bjornvester]

When running on Gradle 6.2, the plugin fails with:

Caused by: groovy.lang.MissingMethodException: No signature of method: static org.gradle.util.SingleMessageLogger.nagUserWith() is applicable for argument types: (String, String, String, null) values: [dependencyUpdates.resolutionSt
rategy, , Remove the assignment operator, '=', when setting this task property, ...]
        at com.github.benmanes.gradle.versions.updates.DependencyUpdatesTask.dependencyUpdates(DependencyUpdatesTask.groovy:81)
[...]

The Gradle class SingleMessageLogger has been rewritten, and should probably not be used anymore (it looks like it is only there for backwards compatibility with the Nebula plugin).

The only replacement is org.gradle.internal.deprecation.DeprecationLogger, which, being an internal class, is not great either.

[bjornvester]

I just realized that the failure for me was triggered by a deprecated way of configuring resolutionStrategy and the issue can be worked around by doing it the new way. But the plugin should still not fail like this.

Reproducer:

dependencyUpdates {
    resolutionStrategy = { }
}