Fix hologram text serialization for 1.8

[giqnt]

Hologram text was displaying as raw JSON strings in Minecraft 1.8 and earlier versions. This occurred because the legacy serialization path was using AdventureSerializer.asJson() which output JSON format that older clients couldn't properly parse.

[giqnt]

this is how it looked before this fix

[Pyrbu]

Have you tested this on a version like 1.12?

[giqnt]

legacySerialization is true only when the server version is lower than 1.9 so it should work