Add maven-enforcer-plugin

Used to enfoce the minimum Maven version 3.0.4 to keep the compability
with plugins.

The CI builds have been adapted to match the new enforcer rules.

GH-17

.travis.yml

@@ -8,15 +8,22 @@
 # +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 #
 # [References]
-# Travis CI Documentation
-#   (https://docs.travis-ci.com)
+# Travis CI
+#   https://docs.travis-ci.com
 language: java
+dist: trusty
+sudo: false
 jdk:
+  - openjdk8
   - oraclejdk8
-sudo: false
 cache:
  directories:
     - $HOME/.m2
+notifications:
+  email:
+    on_success: never
+    on_failure: change
+before_script: mvn --version
+script: mvn -B clean verify -P code-coverage
 after_success:
   - bash <(curl -s https://codecov.io/bash)
-script: mvn -B clean verify -P code-coverage

circle.yml

@@ -9,7 +9,7 @@
 #
 # [References]
 # Circle CI
-#   (https://circleci.com/docs)
+#   https://circleci.com/docs
 machine:
   java:
     version: oraclejdk8
@@ -18,6 +18,10 @@ general:
   artifacts:
     - ./target/*.jar
 
+dependencies:
+  post:
+    - mvn --version
+
 test:
   post:
     - mkdir -p $CIRCLE_TEST_REPORTS/junit/

pom.xml

@@ -70,6 +70,7 @@
     <assembly.descriptor.bin>${basedir}/src/main/assets/assembly-bin.xml</assembly.descriptor.bin>
     <java.version>1.8</java.version>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <maven.version.min>3.0.4</maven.version.min>
 
     <checkstyle.version>8.0</checkstyle.version>
     <junit.version>4.12</junit.version>
@@ -223,6 +224,30 @@
           </execution>
         </executions>
       </plugin>
+
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-enforcer-plugin</artifactId>
+        <version>1.4.1</version>
+        <executions>
+          <execution>
+            <id>enforce-versions</id>
+            <goals>
+              <goal>enforce</goal>
+            </goals>
+            <configuration>
+              <rules>
+                <requireMavenVersion>
+                  <version>(${maven.version.min},)</version>
+                </requireMavenVersion>
+                <requireJavaVersion>
+                  <version>${java.version}</version>
+                </requireJavaVersion>
+              </rules>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
     </plugins>
   </build>