better conversion instructions, add missing $

Author: okko

bin/compile

@@ -50,35 +50,35 @@ if [ -n "$NGINX_VERSION" ] || [ -n "$PHP_VERSION" ] || [ -n "$WORDPRESS_VERSION"
   echo "Rename/remove the variables and then push again:"
   echo ""
   if [ -n "$NGINX_VERSION" ]; then
-      if [-z "BUILDPACK_NGINX_VERSION" ]; then
+      if [-z "$BUILDPACK_NGINX_VERSION" ]; then
           echo "    heroku config:set   BUILDPACK_NGINX_VERSION=$NGINX_VERSION"
       fi
       echo "    heroku config:unset NGINX_VERSION"
   fi
 
   if [ -n "$PHP_VERSION" ]; then
-      if [-z "BUILDPACK_PHP_VERSION" ]; then
+      if [-z "$BUILDPACK_PHP_VERSION" ]; then
           echo "    heroku config:set   BUILDPACK_PHP_VERSION=$PHP_VERSION"
       fi
       echo "    heroku config:unset PHP_VERSION"
   fi
 
   if [ -n "$WORDPRESS_VERSION" ]; then
-      if [-z "BUILDPACK_WORDPRESS_VERSION" ]; then
+      if [-z "$BUILDPACK_WORDPRESS_VERSION" ]; then
           echo "    heroku config:set   BUILDPACK_WORDPRESS_VERSION=$WORDPRESS_VERSION"
       fi
       echo "    heroku config:unset WORDPRESS_VERSION"
   fi
 
   if [ -n "$S3_BUCKET" ]; then
-      if [-z "BUILDPACK_S3_BUCKET" ]; then
+      if [-z "$BUILDPACK_S3_BUCKET" ]; then
           echo "    heroku config:set   BUILDPACK_S3_BUCKET=$S3_BUCKET"
       fi
       echo "    heroku config:unset S3_BUCKET"
   fi
 
-  if [ -n "WORDPRESS_DIR" ]; then
-      if [-z "BUILDPACK_WORDPRESS_DIR" ]; then
+  if [ -n "$WORDPRESS_DIR" ]; then
+      if [-z "$BUILDPACK_WORDPRESS_DIR" ]; then
           echo "    heroku config:set   BUILDPACK_WORDPRESS_DIR=$WORDPRESS_DIR"
       fi
       echo "    heroku config:unset WORDPRESS_DIR"