plugins/textmate: use _command_exists

Addresses bash-it/bash-it#1632

plugins/available/textmate.plugin.bash

@@ -1,7 +1,9 @@
+# shellcheck shell=bash
 cite about-plugin
 about-plugin 'set textmate as a default editor'
 
-if $(command -v mate &> /dev/null) ; then
-  export EDITOR="$(which mate) -w"
-  export GIT_EDITOR=$EDITOR
+if _command_exists mate; then
+	EDITOR="$(type -p mate) -w"
+	GIT_EDITOR="$EDITOR"
+	export EDITOR GIT_EDITOR
 fi