Docker: Use working directory instead of hardcoded dist version

- By using the current (.) working directory, we can get the latest changes in the Docker image.
  If the building of Docker images is automated, it will automatically pick up the checked out version.
- Rearrange some Docker layers things that don't invalidate that much.

.gitignore

@@ -1,8 +1,11 @@
 /node_modules
 /public/storage
-/vendor
 Homestead.json
 Homestead.yaml
 .env
 public/google*.html
 report.html
+
+### Composer ###
+composer.phar
+/vendor/