RATIS-54. Bump maven.min.version to 3.3.9.

BUILDING.md

@@ -13,8 +13,10 @@
 -->
 
 # Building
-Apache Ratis uses Apache Maven for the builds. A 3.2+ version of Maven is required as well as
-at least Java-1.8.
+Apache Ratis uses Apache Maven to build the artifacts.
+It is required to have Maven 3.3.9 or later.
+Apache Ratis is written in Java 8.
+Therefore, it as well requires Java 8 or later.
 
 When building Ratis the first time, shaded files need to be generated by the following command:
 ```

pom.xml

@@ -142,21 +142,23 @@
     <maven-install-plugin.version>2.5.1</maven-install-plugin.version>
     <maven-jar-plugin.version>3.0.2</maven-jar-plugin.version>
     <maven-javadoc-plugin.version>2.10.3</maven-javadoc-plugin.version>
+    <maven-pdf-plugin.version>1.2</maven-pdf-plugin.version>
     <maven-resources-plugin.version>2.6</maven-resources-plugin.version>
     <maven-shade-plugin.version>2.4.3</maven-shade-plugin.version>
     <maven-site-plugin.version>3.5</maven-site-plugin.version>
     <maven-source-plugin.version>2.3</maven-source-plugin.version>
     <maven-stylus-skin.version>1.5</maven-stylus-skin.version>
     <maven-surefire-plugin.version>2.19.1</maven-surefire-plugin.version>
     <maven-xolstice-plugin.version>0.5.0</maven-xolstice-plugin.version>
-    <maven-pdf-plugin.version>1.2</maven-pdf-plugin.version>
+
+    <apache-rat-plugin.version>0.10</apache-rat-plugin.version>
     <build-helper-maven-plugin.version>1.9</build-helper-maven-plugin.version>
     <exec-maven-plugin.version>1.3.1</exec-maven-plugin.version>
+    <findbugs.version>3.0.0</findbugs.version>
     <make-maven-plugin.version>1.0-beta-1</make-maven-plugin.version>
     <native-maven-plugin.version>1.0-alpha-8</native-maven-plugin.version>
-    <findbugs.version>3.0.0</findbugs.version>
-    <apache-rat-plugin.version>0.10</apache-rat-plugin.version>
     <wagon-ssh.version>1.0</wagon-ssh.version>
+
     <shell-executable>bash</shell-executable>
 
     <hadoop.version>3.0.0-alpha1</hadoop.version>
@@ -165,7 +167,7 @@
     <!-- define the Java language version used by the compiler -->
     <javac.version>1.8</javac.version>
     <java.min.version>${javac.version}</java.min.version>
-    <maven.min.version>3.0.4</maven.min.version>
+    <maven.min.version>3.3.9</maven.min.version>
 
     <!--Version of protobuf to be shaded -->
     <shaded.protobuf.version>3.1.0</shaded.protobuf.version>
@@ -408,10 +410,10 @@
           <configuration>
             <rules>
               <requireMavenVersion>
-                <version>[3.0.2,)</version>
+                <version>[${maven.min.version},)</version>
               </requireMavenVersion>
               <requireJavaVersion>
-                <version>[1.8,)</version>
+                <version>[${java.min.version},)</version>
               </requireJavaVersion>
             </rules>
           </configuration>