Bump min_minetest_version to "5.5.0" (#17)

closes #16

mod.conf

@@ -1,4 +1,4 @@
 name = unifieddyes
 description = Unified Dyes expands the standard dye set from 15 to 90 colors.
 optional_depends = default, dye, basic_materials
-min_minetest_version = 5.3.0
+min_minetest_version = 5.5.0