Go use reflection-remapper instead. It has the same featureset, with support for mojang mappings. This wont be updated probably ever.
An easy way to work with nms, without the hassle of importing spigot.
Please see the wiki for documentation on how to use the plugin. You can also see an example plugin for more examples.
This library can be found on JitPack for easy integration into maven projects.
<repositories>
<repository>
<id>jitpack.io</id>
<url>https://jitpack.io</url>
</repository>
</repositories>
<dependencies>
<dependency>
<groupId>com.github.theminecoder</groupId>
<artifactId>NMSProxy</artifactId>
<version>0.3</version>
<scope>provided</scope>
</dependency>
</dependencies>