Add missing implicitly used dependency

Author: atextor

core/esmf-aspect-model-validator/pom.xml

@@ -66,6 +66,10 @@
          <artifactId>lombok</artifactId>
          <scope>provided</scope>
       </dependency>
+      <dependency>
+         <groupId>org.slf4j</groupId>
+         <artifactId>slf4j-api</artifactId>
+      </dependency>
 
       <!-- Test dependencies -->
       <dependency>