Use DOKKU_ROOT instead of HOME.

HOME is not consistent if dokku is ran e.g. as root (for setup).
The DOKKU_ROOT variable will also make it possible to have the repositories stored in an arbitrary location (works-ish right now)

plugins/git/commands

@@ -18,14 +18,14 @@ case "$1" in
 
   git-*)
     APP="$(echo $2 | perl -pe 's/(?<!\\)'\''//g' | sed 's/\\'\''/'\''/g')"
-    APP_PATH=$HOME/$APP
+    APP_PATH=$DOKKU_ROOT/$APP
 
     if [[ $1 == "git-receive-pack" && ! -d $APP_PATH ]]; then
         git init --bare $APP_PATH > /dev/null
         PRERECEIVE_HOOK="$APP_PATH/hooks/pre-receive"
         cat > $PRERECEIVE_HOOK <<EOF
 #!/bin/bash
-cat | dokku git-hook $APP
+cat | DOKKU_ROOT="$DOKKU_ROOT" dokku git-hook $APP
 EOF
         chmod +x $PRERECEIVE_HOOK
     fi