You're missing the trailing letter s
in groupId
of the plugin. Correct declaration should be:
<dependency>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-release-plugin</artifactId>
<version>2.1</version>
</dependency>
I'd also consider upgrading to a fresher version. As far as I can see, current version is 2.4.1.