Include slf4j-jdk14 during tests.

core/pom.xml

@@ -476,6 +476,11 @@ THE SOFTWARE.
       <groupId>org.slf4j</groupId>
       <artifactId>log4j-over-slf4j</artifactId>
     </dependency>
+    <dependency>
+      <groupId>org.slf4j</groupId>
+      <artifactId>slf4j-jdk14</artifactId>
+      <scope>test</scope>
+    </dependency>
     <dependency>
       <groupId>com.sun.xml.txw2</groupId>
       <artifactId>txw2</artifactId>