Update robots.txt reflecting actual folders (#3625)

* Update robots.txt

"grav" folder no longer exists

* Add folders now existing

robots.txt

@@ -1,16 +1,21 @@
 User-agent: *
+Disallow: /.github/
+Disallow: /.phan/
+Disallow: /assets/
 Disallow: /backup/
 Disallow: /bin/
 Disallow: /cache/
-Disallow: /grav/
 Disallow: /logs/
 Disallow: /system/
-Disallow: /vendor/
+Disallow: /tests/
+Disallow: /tmp/
 Disallow: /user/
+Disallow: /vendor/
+Disallow: /webserver-configs/
 Allow: /user/pages/
 Allow: /user/themes/
 Allow: /user/images/
 Allow: /
 Allow: *.css$
 Allow: *.js$
-Allow: /system/*.js$
+Allow: /system/*.js$