README_DEV.md

• buffer is kept at 5.6.1 because the whole point of it being there to begin with is to check if waxing is compatible with the buffer polyfill in non-node environments, including old ones, and there was a bug (feross/buffer#251) fixed in 5.7.0 that waxing should work around
• file-type fixed to @16 because 17 is ESM only