zsh-autosuggestions: update to 0.6.3.

## v0.6.3
- Fixed bug moving cursor to end of buffer after accepting suggestion (#453)

## v0.6.2
- Fixed bug deleting the last character in the buffer in vi mode (#450)
- Degrade gracefully when user doesn't have `zsh/system` module installed (#447)

## v0.6.1
- Fixed bug occurring when `_complete` had been aliased (#443)

## v0.6.0
- Added `completion` suggestion strategy powered by completion system (#111)
- Allow setting `ZSH_AUTOSUGGEST_BUFFER_MAX_SIZE` to an empty string (#422)
- Don't fetch suggestions after copy-earlier-word (#439)
- Allow users to unignore zle-\* widgets (e.g. zle-line-init) (#432)

(wiz)