Upgrade maven-enforcer-plugin 3.3.0 -> 3.4.0 (#759)

See:
- https://github.com/apache/maven-enforcer/releases/tag/enforcer-3.4.0
- apache/maven-enforcer@enforcer-3.3.0...enforcer-3.4.0

pom.xml

@@ -976,7 +976,7 @@
                 <plugin>
                     <groupId>org.apache.maven.plugins</groupId>
                     <artifactId>maven-enforcer-plugin</artifactId>
-                    <version>3.3.0</version>
+                    <version>3.4.0</version>
                     <configuration>
                         <fail>false</fail>
                         <rules>
@@ -1015,19 +1015,9 @@
                             </banDuplicateClasses>
                             <banDuplicatePomDependencyVersions />
                             <banDynamicVersions>
-                                <!-- XXX: Drop this once the `ignores` section
-                                below works as expected. -->
-                                <allowSnapshots>true</allowSnapshots>
-                                <!-- XXX: It shouldn't be necessary to specify
-                                an empty `excludedScopes` parameter, but
-                                without this an NPE results. See
-                                https://issues.apache.org/jira/browse/MENFORCER-481. -->
-                                <excludedScopes />
-                                <!-- XXX: This doesn't work. See
-                                https://issues.apache.org/jira/browse/MENFORCER-480.
                                 <ignores>
                                     <ignore>${project.groupId}</ignore>
-                                </ignores> -->
+                                </ignores>
                             </banDynamicVersions>
                             <dependencyConvergence />
                             <enforceBytecodeVersion>