Revert "Update the Maven release plugin for compatibility with Maven 3.3"

This reverts commit 4a90ef6.

Author: phillipuniverse

pom.xml

@@ -213,7 +213,11 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-release-plugin</artifactId>
-                <version>2.5.6</version>
+                <version>2.2.1</version>
+                <configuration>
+                    <!-- Only here for the Spock SNAPSHOT dependency since it has not been fully released -->
+                    <allowTimestampedSnapshots>true</allowTimestampedSnapshots>
+                </configuration>
             </plugin>
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>