Fix bad filenames (#856)

Author: iHiD

exercises/practice/bottle-song/.meta/config.json

@@ -4,13 +4,13 @@
   ],
   "files": {
     "solution": [
-      "./bottle-song.lisp"
+      "bottle-song.lisp"
     ],
     "test": [
-      "./bottle-song-test.lisp"
+      "bottle-song-test.lisp"
     ],
     "example": [
-      "./.meta/example.lisp"
+      ".meta/example.lisp"
     ]
   },
   "blurb": "Produce the lyrics to the popular children's repetitive song: Ten Green Bottles.",