change robot to robots in static paths list (#5).

It looks like the caveman2 project generator has a typo regarding the robots.txt
file in the static file and paths list (in app.lisp file). The list has 'robot'
instead of 'robots' in it. This means the search engine crawlers can't reach the
robots.txt file because the site returns a 404. This change fixes that.

app.lisp

@@ -22,7 +22,7 @@
 	 (builder
 	  (:static
 	   :path (lambda (path)
-		   (if (ppcre:scan "^(?:/images/|/css/|/js/|/robot\\.txt$|/favicon\\.ico$)" path)
+		   (if (ppcre:scan "^(?:/images/|/css/|/js/|/robots\\.txt$|/favicon\\.ico$)" path)
 		       path
 		       nil))
 	   :root *static-directory*)