Replace exa with eza (#301)

Exa is deprecated and replaced with eza. See ogham/exa#1243

docs/man/zi.1

@@ -408,7 +408,7 @@ zi creinstall %HOME/my_completions
 .RS 2
 .nf
 # For GNU ls (the binaries can be gls, gdircolors, e.g. on OS X when installing the
-# coreutils package from Homebrew; you can also use https://github.com/ogham/exa)
+# coreutils package from Homebrew; you can also use https://github.com/eza-community/eza)
 zi ice atclone"dircolors -b LS_COLORS > c.zsh" atpull'%atclone' pick"c.zsh" nocompile'!'
 zi light trapd00r/LS_COLORS
 .fi

lib/zsh/autoload.zsh

@@ -2865,8 +2865,8 @@ EOF
 .zi-ls() {
   if (( ${+commands[tree]} )); then
     ZI[TREE]="${commands[tree]} -L 3 -C --charset utf-8"
-  elif (( ${+commands[exa]} )); then
-    ZI[TREE]="${commands[exa]} --color=always -T -l -L3"
+  elif (( ${+commands[eza]} )); then
+    ZI[TREE]="${commands[eza]} --color=always -T -l -L3"
   else
     builtin print "${ZI[col-error]}No \`tree' program, it is required by the subcommand \`ls\'${ZI[col-rst]}"
     builtin print "Download from: http://mama.indstate.edu/users/ice/tree/"