Use `#!/bin/sh` for portability (#14)

yadm

@@ -1,5 +1,4 @@
-#!/usr/bin/env bash
-
+#!/bin/sh
 # yadm - Yet Another Dotfiles Manager
 # Copyright (C) 2015  Tim Byrne
 
@@ -15,6 +14,11 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+#; execute script with bash (shebang line is /bin/sh for portability)
+if [ -z "$BASH_VERSION" ]; then
+  [ "$YADM_TEST" != 1 ] && exec bash "$0" "$@"
+fi
+
 VERSION=1.04
 
 YADM_WORK="$HOME"