Revert "[maven-release-plugin] prepare release 2.1.1"

This reverts commit 2c9c4c2.

Author: sebastianchristopher

pom.xml

@@ -4,7 +4,7 @@
 
   <groupId>uk.ac.ox.ctl</groupId>
   <artifactId>canvas-api</artifactId>
-  <version>2.1.1</version>
+  <version>2.1.1-SNAPSHOT</version>
   <packaging>jar</packaging>
 
   <name>Canvas API Library</name>
@@ -39,7 +39,7 @@
     <connection>scm:git:ssh://git@github.com/oxctl/canvas-api.git</connection>
     <developerConnection>scm:git:ssh://git@github.com/oxctl/canvas-api.git</developerConnection>
     <url>https://github.com/oxctl/canvas-api</url>
-    <tag>2.1.1</tag>
+    <tag>HEAD</tag>
   </scm>
 
   <build>