Purpur blocks aren't being converted

[kolakz]

On 1.8, purpur blocks are glitched because there is no conversion for it yet. As a result, I can't move when stepping on it.

Steps to reproduce the behavior:

1. Create a 1.16 server
2. Place some purpur blocks
3. Log on 1.8
4. Step on the purpur block
5. You shouldn't be able to move

ViaVersion Dump: https://dump.viaversion.com/77ff17c50368696c0073b35a2b20b0319bc380573717551a498fcb40e597d28d

Checklist (mark with [X] to check)

• [x] I have included a ViaVersion dump
• [ ] If applicable, I have included a paste (not a screenshot) of the error
• [x] I have tried a build from https://ci.viaversion.com/ and the issue still persists
• [ ] I have looked at https://www.spigotmc.org/resources/viarewind-legacy-support.52924/ and it does not offer a fix for my problem

[FormallyMyles]

Use latest builds as written in the checklist,

-- https://github.com/ViaVersion/ViaRewind/pull/309