weechatScripts.wee-slack: 2.4.0 -> 2.5.0

wee-slack now (optionally) depends on a data file called weemoji.json
that allows it to translate between Slack emoji names (like
"slight_smile") and Unicode codepoints. For convenience, the derivation
now installs this file and patches the script so that the user doesn't
need to do any extra configuration to use it.