Switch Maven build to gmavenplus plugin and bump dependency versions

pom.xml

@@ -14,15 +14,14 @@
   </properties>
 
   <build>
-    <!-- Mandatory plugins for using Spock -->
     <plugins>
+      <!-- Mandatory plugins for using Spock -->
       <plugin>
-        <groupId>org.codehaus.gmaven</groupId>
-        <artifactId>gmaven-plugin</artifactId>
+        <!-- The gmavenplus plugin is used to compile Groovy code. To learn more about this plugin, 
+        visit https://github.com/groovy/GMavenPlus/wiki -->
+        <groupId>org.codehaus.gmavenplus</groupId>
+        <artifactId>gmavenplus-plugin</artifactId>
         <version>1.4</version>
-        <configuration>
-          <providerSelection>2.0</providerSelection>
-        </configuration>
         <executions>
           <execution>
             <goals>
@@ -31,27 +30,9 @@
             </goals>
           </execution>
         </executions>
-        <dependencies>
-          <dependency>
-            <groupId>org.codehaus.gmaven.runtime</groupId>
-            <artifactId>gmaven-runtime-2.0</artifactId>
-            <version>1.4</version>
-            <exclusions>
-              <exclusion>
-                <groupId>org.codehaus.groovy</groupId>
-                <artifactId>groovy-all</artifactId>
-              </exclusion>
-            </exclusions>
-          </dependency>
-          <dependency>
-            <groupId>org.codehaus.groovy</groupId>
-            <artifactId>groovy-all</artifactId>
-            <version>2.3.8</version>
-          </dependency>
-        </dependencies>
       </plugin>
       <!-- Optional plugins for using Spock -->
-   <!-- Only required if default Surefire configuration is not satisfactory -->
+      <!-- Only required if names of spec classes don't match default Surefire patterns (`*Test` etc.) -->
       <plugin>
         <artifactId>maven-surefire-plugin</artifactId>
         <version>2.6</version>
@@ -82,6 +63,11 @@
       <scope>test</scope>
     </dependency>
     <!-- Optional dependencies for using Spock -->
+    <dependency> <!-- use a specific Groovy version rather than the one specified by spock-core -->
+      <groupId>org.codehaus.groovy</groupId>
+      <artifactId>groovy-all</artifactId>
+      <version>2.3.10</version>
+    </dependency>
     <dependency> <!-- enables mocking of classes (in addition to interfaces) -->
       <groupId>cglib</groupId>
       <artifactId>cglib-nodep</artifactId>
@@ -94,17 +80,17 @@
       <version>2.1</version>
       <scope>test</scope>
     </dependency>
-    <dependency> <!-- only necessary if Hamcrest matchers are used -->
+    <dependency> <!-- only required if Hamcrest matchers are used -->
       <groupId>org.hamcrest</groupId>
       <artifactId>hamcrest-core</artifactId>
       <version>1.3</version>
       <scope>test</scope>
     </dependency>
-<!-- Dependencies used by examples in this project (not required for using Spock) -->
+    <!-- Dependencies used by examples in this project (not required for using Spock) -->
     <dependency>
       <groupId>com.h2database</groupId>
       <artifactId>h2</artifactId>
-      <version>1.4.182</version>
+      <version>1.4.185</version>
     </dependency>
   </dependencies>
 
@@ -119,17 +105,6 @@
     </repository>
   </repositories>
 
-  <!-- Only required if a snapshot version of Spock's Maven plugin is used -->
-  <pluginRepositories>
-    <pluginRepository>
-      <id>spock-snapshots</id>
-      <url>https://oss.sonatype.org/content/repositories/snapshots/</url>
-      <snapshots>
-        <enabled>true</enabled>
-      </snapshots>
-    </pluginRepository>
-  </pluginRepositories>
-
   <!-- Only required in spock-example build -->
   <distributionManagement>
     <repository>