Update Velocity Version in doc -> 3.4.0-SNAPSHOT

[Timongcraft]

The download page and some parts of the docs still use the older 3.3.0-SNAPSHOT version of Velocity, while that updated 3 weeks ago. (fixed)

Parts of the doc that seem to be affected:

• https://docs.papermc.io/velocity/getting-started#after-launch
• https://docs.papermc.io/velocity/faq#what-version-of-java-does-velocity-require (should say 3.3.x and above)
• https://docs.papermc.io/velocity/dev/porting-plugins-from-velocity-1#minimum-supported-java-version-bump (should say 3.3.x and above)