fix: don't use `$functions_source` for compatibility with zsh < 5.4

plugins/aliases/aliases.plugin.zsh

-# with lots of 3rd-party amazing aliases installed, just need something to explore it quickly.
-#
-# - acs: alias cheatsheet
-#   group alias by command, pass addition argv to grep.
-function acs(){
+# Handle $0 according to the standard:
+# https://zdharma-continuum.github.io/Zsh-100-Commits-Club/Zsh-Plugin-Standard.html
+0="${${ZERO:-${0:#$ZSH_ARGZERO}}:-${(%):-%N}}"
+0="${${(M)0:#/*}:-$PWD/$0}"
+
+eval '
+  function acs(){
     (( $+commands[python3] )) || {
       echo "[error] No python executable detected"
       return
     }
-  alias | python3 ${functions_source[$0]:h}/cheatsheet.py $@
-}
+    alias | python3 "'"${0:h}"'/cheatsheet.py" "$@"
+  }
+'

plugins/shell-proxy/shell-proxy.plugin.zsh

 #!/usr/bin/bash
 # shellcheck disable=SC1090,SC2154
 
-proxy() {
+# Handle $0 according to the standard:
+# https://zdharma-continuum.github.io/Zsh-100-Commits-Club/Zsh-Plugin-Standard.html
+0="${${ZERO:-${0:#$ZSH_ARGZERO}}:-${(%):-%N}}"
+0="${${(M)0:#/*}:-$PWD/$0}"
+
+eval '
+  proxy() {
     # deprecate $DEFAULT_PROXY, use SHELLPROXY_URL instead
     if [[ -n "$DEFAULT_PROXY" && -z "$SHELLPROXY_URL" ]]; then
       echo >&2 "proxy: DEFAULT_PROXY is deprecated, use SHELLPROXY_URL instead"
@@ -17,7 +23,7 @@ proxy() {
     fi
 
     # the proxy.py script is in the same directory as this function
-  local proxy="${functions_source[$0]:A:h}/proxy.py"
+    local proxy="'"${0:h}"'/proxy.py"
 
     # capture the output of the proxy script and bail out if it fails
     local output
@@ -26,7 +32,8 @@ proxy() {
 
     # evaluate the output generated by the proxy script
     source <(echo "$output")
-}
+  }
+'
 
 _proxy() {
   local -r commands=('enable' 'disable' 'status')