This change improves performance for those using the logging operations of Reactor.

The old implementation usedString#replaceFirst as it's method to replace the package name with an empty String. AsreplaceFirst accepts a regular expression, the evaluation was more expensive.
The new logic utilizes a simple substring search and doesn't create an unnecessary new String, but directly appends to the StringBuilder.

Additionally each dot (.) in the package's name, including the appended dot at the end, was treated as a wildcard, which is unexpected behaviour (i assume).