Small change to encoder element.

I have logback.xml that does not have a pattern in the <encoder> section:

                <encoder class="ch.qos.logback.core.encoder.LayoutWrappingEncoder">
                        <layout class="ch.qos.logback.classic.PatternLayout">
                                <param name="Pattern" value="%date{HH:mm:ss.SSS}::%-4relative::%thread::%-5level::%c::%msg%n" />
                        </layout>
                </encoder>