Add support for DOKKU_TAG in bootstrap.sh

Fixes #330
Refs #329

bootstrap.sh

@@ -5,15 +5,23 @@ export DOKKU_REPO=${DOKKU_REPO:-"https://github.com/progrium/dokku.git"}
 
 if ! which apt-get &>/dev/null
 then
-	echo "This installation script requires apt-get. For manual installation instructions, consult https://github.com/progrium/dokku ."
-	exit 1
+  echo "This installation script requires apt-get. For manual installation instructions, consult https://github.com/progrium/dokku ."
+  exit 1
 fi
 
 apt-get update
 apt-get install -y git make curl software-properties-common
 
 cd ~ && test -d dokku || git clone $DOKKU_REPO
-cd dokku && test $DOKKU_BRANCH && git checkout origin/$DOKKU_BRANCH || true
+cd dokku
+git fetch origin
+
+if [[ -n $DOKKU_BRANCH ]]; then
+  git checkout origin/$DOKKU_BRANCH
+elif [[ -n $DOKKU_TAG ]]; then
+  git checkout $DOKKU_TAG
+fi
+
 make install
 
 echo