Update maven-enforcer-plugin to 3.0.0-M3 (#3577)

Author: briandealwis

plugins/com.google.cloud.tools.eclipse.appengine.newproject.test/src/com/google/cloud/tools/eclipse/appengine/newproject/CodeTemplatesTest.java

@@ -464,7 +464,7 @@ private Element validatePom() throws ParserConfigurationException, SAXException,
 
     String enforcerVersion =
         (String) xpath.evaluate("string(./m:version)", enforcerNode, XPathConstants.STRING);
-    Assert.assertEquals("3.0.0-M2", enforcerVersion);
+    Assert.assertEquals("3.0.0-M3", enforcerVersion);
     String requiredMavenVersion =
         (String)
             xpath.evaluate(

plugins/com.google.cloud.tools.eclipse.util/templates/appengine/pom.xml.ftl

@@ -88,7 +88,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-enforcer-plugin</artifactId>
-        <version>3.0.0-M2</version>
+        <version>3.0.0-M3</version>
         <executions>
           <execution>
             <id>enforce-maven</id>

pom.xml

@@ -363,7 +363,7 @@
         <plugin>
           <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-enforcer-plugin</artifactId>
-          <version>3.0.0-M2</version>
+          <version>3.0.0-M3</version>
         </plugin>
 
         <plugin>