add slf4j dependency

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1884603 13f79535-47bb-0310-9956-ffa450edef68

src/multimodule/poi/java9/module-info.java

@@ -21,6 +21,7 @@ module org.apache.poi.poi {
     requires commons.math3;
     requires SparseBitSet;
     requires commons.logging;
+    requires org.slf4j;
     requires java.logging;
     requires java.desktop;