[MENFORCER-297] - Upgrade parent to 31

 o Removed property based version definition for maven-plugin-plugin
 o Upgraded extra-enforcer-rules to 1.0-beta-7

maven-enforcer-plugin/pom.xml

@@ -141,7 +141,6 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-plugin-plugin</artifactId>
-        <version>${mavenPluginPluginVersion}</version>
       </plugin>
     </plugins>
   </reporting>
@@ -153,7 +152,6 @@
         <plugins>
           <plugin>
             <artifactId>maven-invoker-plugin</artifactId>
-            <version>2.0.0</version>
             <configuration>
               <debug>true</debug>
               <projectsDirectory>src/it/projects</projectsDirectory>

pom.xml

@@ -23,7 +23,7 @@
   <parent>
     <artifactId>maven-parent</artifactId>
     <groupId>org.apache.maven</groupId>
-    <version>30</version>
+    <version>31</version>
     <relativePath>../pom/maven/pom.xml</relativePath>
   </parent>
   <groupId>org.apache.maven.enforcer</groupId>
@@ -64,7 +64,6 @@
   </distributionManagement>
   <properties>
     <maven.version>3.0</maven.version>
-    <mavenPluginPluginVersion>3.5</mavenPluginPluginVersion>
     <maven.site.path>enforcer-archives/enforcer-LATEST</maven.site.path>
   </properties>
 
@@ -168,11 +167,6 @@
   <build>
     <pluginManagement>
       <plugins>
-        <plugin>
-          <groupId>org.apache.maven.plugins</groupId>
-          <artifactId>maven-plugin-plugin</artifactId>
-          <version>${mavenPluginPluginVersion}</version>
-        </plugin>
         <plugin>
           <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-release-plugin</artifactId>
@@ -191,14 +185,14 @@
       </plugins>
     </pluginManagement>
     <plugins>
-      <plugin> <!-- TODO overriding 1.0-beta-3 from maven-parent-30.pom which fails with https://github.com/mojohaus/extra-enforcer-rules/issues/13 -->
+      <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-enforcer-plugin</artifactId>
         <dependencies>
           <dependency>
             <groupId>org.codehaus.mojo</groupId>
             <artifactId>extra-enforcer-rules</artifactId>
-            <version>1.0-beta-6</version>
+            <version>1.0-beta-7</version>
           </dependency>
         </dependencies>
       </plugin>