As of Nifty 1.4.2 we're targeting a Maven central release. It's not released yet but here are the presumably details:
<groupId>com.github.nifty-gui</groupId>
<artifactId>nifty</artifactId>
<version>1.4.2-SNAPSHOT</version>
You'll still need to add both repositories to your pom.xml for now, at least:
<repositories>
<!-- only needed for snapshot builds starting with 1.4.2-SNAPSHOT -->
<repository>
<id>ossrh</id>
<url>https://oss.sonatype.org/content/repositories/snapshots/</url>
</repository>
<!-- still needed for some other dependencies not yet available in central like jglfont -->
<repository>
<id>nifty-maven-repo.sourceforge.net</id>
<url>http://nifty-gui.sourceforge.net/nifty-maven-repo</url>
</repository>
</repositories>