plugins/direnv: use `_command_exists`

clean_files.txt

@@ -80,6 +80,7 @@ plugins/available/alias-completion.plugin.bash
 plugins/available/autojump.plugin.bash
 plugins/available/basher.plugin.bash
 plugins/available/cmd-returned-notify.plugin.bash
+plugins/available/direnv.plugin.bash
 plugins/available/docker-machine.plugin.bash
 plugins/available/git.plugin.bash
 plugins/available/go.plugin.bash

plugins/available/direnv.plugin.bash

@@ -1,4 +1,7 @@
+# shellcheck shell=bash
 cite about-plugin
 about-plugin 'load direnv, if you are using it: https://direnv.net/'
 
-[ -x "$(which direnv)" ] && eval "$(direnv hook bash)"
+if _command_exists direnv; then
+	eval "$(direnv hook bash)"
+fi