Removed plugin output directory configuration (#300)

The maven-plugin-plugin configuration was causing the output to be
placed in a location that was not being included when the project
was built. This resulted in other projects that depend on
resource-server-plugin to fail to build due to a missing plugin.xml.
Leaving it at it's default location causes the output to live in
classes/META-INF/maven, which gets picked up properly when the jar is
created.

resource-server-plugin/pom.xml

@@ -74,7 +74,6 @@
           <version>3.15.0</version>
           <configuration>
             <goalPrefix>plugin</goalPrefix>
-            <outputDirectory>target/dir</outputDirectory>
           </configuration>
         </plugin>
         <plugin>