update mixin version

[Nischhelm]

since essential takes control over the whole launcher system, it also forces all the mods using its own shaded mixins.

it would be great if you could keep it up to date, as some mods will simply crash when using newer mixins systems like the "unsafe" constructor injections.

you could even remove your own custom constructor injection points then, as mixins provides that now since 0.8.6.

theres probably other spots where the mixin version needs to be changed so this PR is more like a suggestion

[Nischhelm]

issue fixed in fonnymunkey/RLFoliage@354f898 (RLFoliage 2.5.0)
this was a 3 way mod conflict with essential only reloading the environment if kotlin is transformer excluded, which betterfoliage does/did.