Bugfix: `default-command` utilizes $SHELL env var

The `default-command` setting on OS X determines the default shell if
`default-shell` is not set.
This update enables use of any user defined shell, even if
`default-shell` is not set.

Fixes #2

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Changelog
 
 ### master
+- bugfix: determine the default shell from the $SHELL env var on OS X
 
 ### v1.0.0, 2014-07-30
 - initial work on the plugin

sensible.tmux

@@ -67,7 +67,7 @@ main() {
 
 	# required (only) on OS X
 	if is_osx && option_value_not_changed "default-command" ""; then
-		tmux set-option -g default-command "reattach-to-user-namespace -l bash"
+		tmux set-option -g default-command "reattach-to-user-namespace -l $SHELL"
 	fi
 
 	# upgrade $TERM