Merge pull request #36 from apache/slf4j

add undeclared but used SLF4J dependency
diff --git a/pom.xml b/pom.xml
index a9e1c75..f91c663 100644
--- a/pom.xml
+++ b/pom.xml
@@ -90,6 +90,7 @@
     <doxiaSitetoolsVersion>1.9.2</doxiaSitetoolsVersion>
     <javaVersion>7</javaVersion><!-- Because PMD 5.4+ requires Java 7 -->
     <pmdVersion>6.29.0</pmdVersion>
+    <slf4jVersion>1.7.25</slf4jVersion>
     <sitePluginVersion>3.7.1</sitePluginVersion>
     <projectInfoReportsPluginVersion>3.0.0</projectInfoReportsPluginVersion>
     <project.build.outputTimestamp>2020-10-24T17:10:38Z</project.build.outputTimestamp>
@@ -133,17 +134,17 @@
       <version>3.1.0</version>
     </dependency>
     <dependency>
-        <groupId>org.apache.maven</groupId>
-        <artifactId>maven-embedder</artifactId>
-        <version>3.1.0</version>
-        <scope>provided</scope>
+      <groupId>org.apache.maven</groupId>
+      <artifactId>maven-embedder</artifactId>
+      <version>3.1.0</version>
+      <scope>provided</scope>
     </dependency>
 
     <!-- pmd -->
     <dependency>
-        <groupId>org.apache.commons</groupId>
-        <artifactId>commons-lang3</artifactId>
-        <version>3.8.1</version>
+      <groupId>org.apache.commons</groupId>
+      <artifactId>commons-lang3</artifactId>
+      <version>3.8.1</version>
     </dependency>
     <dependency>
       <groupId>net.sourceforge.pmd</groupId>
@@ -166,11 +167,16 @@
       <version>${pmdVersion}</version>
     </dependency>
 
+    <dependency>
+      <groupId>org.slf4j</groupId>
+      <artifactId>slf4j-api</artifactId>
+      <version>${slf4jVersion}</version>
+    </dependency>
     <!-- Support logging of PMD through slf4j. See also MPMD-244 -->
     <dependency>
-        <groupId>org.slf4j</groupId>
-        <artifactId>jul-to-slf4j</artifactId>
-        <version>1.7.25</version>
+      <groupId>org.slf4j</groupId>
+      <artifactId>jul-to-slf4j</artifactId>
+      <version>${slf4jVersion}</version>
     </dependency>
 
     <!-- doxia -->
@@ -252,7 +258,7 @@
     <dependency>
       <groupId>org.slf4j</groupId>
       <artifactId>slf4j-simple</artifactId>
-      <version>1.7.5</version>
+      <version>${slf4jVersion}</version>
       <scope>test</scope>
     </dependency>
   </dependencies>