[maven-release-plugin] prepare for next development iteration

Author: headius

pom.xml

@@ -10,7 +10,7 @@
   <groupId>com.github.jnr</groupId>
   <artifactId>jnr-posix</artifactId>
   <packaging>jar</packaging>
-  <version>3.1.19</version>
+  <version>3.1.20-SNAPSHOT</version>
   <name>jnr-posix</name>
   <description>
     Common cross-project/cross-platform POSIX APIs