[reload4j] default branch changed from "branch_1.2.18" to "master"

[Ceki Gülcü]

Hello all,

Given that releases with a 4th segment such as 1.2.18.5 cause problems
in some environments such as OSGi, we will follow a 3 segment
versioning. For example, the next version will be 1.2.19 instead of
1.2.18.6.

Thus, it no longer makes sense to have the default branch as
"branch_1.2.18".

Best regards,

-- 
Ceki Gülcü

Sponsoring SLF4J/logback/reload4j at https://github.com/sponsors/qos-ch