Add slf4j-api pom for nameserver and broker (#257)

broker/pom.xml

@@ -68,6 +68,10 @@
             <groupId>org.javassist</groupId>
             <artifactId>javassist</artifactId>
         </dependency>
+        <dependency>
+            <groupId>org.slf4j</groupId>
+            <artifactId>slf4j-api</artifactId>
+        </dependency>
     </dependencies>
 
     <build>

namesrv/pom.xml

@@ -48,5 +48,9 @@
             <groupId>ch.qos.logback</groupId>
             <artifactId>logback-core</artifactId>
         </dependency>
+        <dependency>
+            <groupId>org.slf4j</groupId>
+            <artifactId>slf4j-api</artifactId>
+        </dependency>
     </dependencies>
 </project>