Project is mavenized!

Hello! This little change is making a lot of easier developers to keep Updater code in their plugins up-to-date!

I've setted up my own Jenkins to automatically build it from here (my from my fork but after you accept my Pull Request - yours code).

Any developer can add it into his project by adding this lines into pom.xml:
```
<repositories>
	...
	<repository>
		<id>voxile.ru</id>
		<url>http://ci.voxile.ru/plugin/repository/everything/</url>
	</repository>
	...
</repositories>
...
<dependencies>
	...
	<dependency>
		<groupId>net.gravitydevelopment</groupId>
		<artifactId>Updater</artifactId>
		<version>2.0</version>
	</dependency>
	...
</dependencies>
```
And setup shading it into .jar.