add dependency that contains InstrumentedAppender

Author: jkremser

pom.xml

@@ -139,6 +139,11 @@
                 <artifactId>simpleclient_hotspot</artifactId>
                 <version>${prometheus.metrics.version}</version>
             </dependency>
+            <dependency>
+                <groupId>io.prometheus</groupId>
+                <artifactId>simpleclient_log4j</artifactId>
+                <version>${prometheus.metrics.version}</version>
+            </dependency>
             <dependency>
                 <groupId>org.slf4j</groupId>
                 <artifactId>slf4j-api</artifactId>