Sync the reverse-string exercise's metadata with the latest data.

exercises/practice/reverse-string/.meta/config.json

@@ -13,7 +13,7 @@
       ".meta/example.v"
     ]
   },
-  "blurb": "Reverse a string.",
+  "blurb": "Reverse a given string.",
   "source": "Introductory challenge to reverse an input string",
   "source_url": "https://medium.freecodecamp.org/how-to-reverse-a-string-in-javascript-in-3-different-ways-75e4763c68cb"
 }