pom: rename maven-central repositories to central
pom: rename maven-central repositories to central

This is the name maven internally uses. Currently the effective pom
looks like maven-central -> runelite -> central, which doesn't make
sense since maven-central and central are the same. With this, the
effective pom is central -> runelite.

runelite/runelite,runelite/runelite,runelite/runelite