completion: Avoid aliases with `command ls`

If the user has an alias overriding the `ls` command that modifies the
output (e.g. `alias ls='ls -F'`), it will cause unexpected characters to
appear in completions. Using `command ls` forces the shell to use the
command directly, without alias expansion.

This also blackholes the stderr of `ls` when used to avoid printing
errors during completion if the requisite directory does not exist.

completions/bash/brew

@@ -52,7 +52,7 @@ __brew_complete_formulae() {
 
 __brew_complete_installed() {
   local cur="${COMP_WORDS[COMP_CWORD]}"
-  local inst="$(ls "$(brew --cellar)")"
+  local inst="$(command ls "$(brew --cellar)" 2>/dev/null)"
   COMPREPLY=($(compgen -W "$inst" -- "$cur"))
 }
 
@@ -71,7 +71,7 @@ __brew_complete_versions() {
 
 __brew_complete_logs() {
   local cur="${COMP_WORDS[COMP_CWORD]}"
-  local logs="$(ls "${HOMEBREW_LOGS:-~/Library/Logs/Homebrew/}")"
+  local logs="$(command ls "${HOMEBREW_LOGS:-${HOME}/Library/Logs/Homebrew/}" 2>/dev/null)"
   COMPREPLY=($(compgen -W "$logs" -- "$cur"))
 }