fix(challenges): a sentence didn't make sense, so I modified it

lalov1 · scissorsneedfoodtoo · commit 3d7792049a6e · 2018-09-06T17:52:38.000+09:00
ISSUES CLOSED: #18046
diff --git a/challenges/02-javascript-algorithms-and-data-structures/debugging.json b/challenges/02-javascript-algorithms-and-data-structures/debugging.json
@@ -117,7 +117,7 @@
       "id": "587d7b84367417b2b2512b34",
       "title": "Use typeof to Check the Type of a Variable",
       "description": [
-        "You can use <code>typeof</code> to check the data structure, or type, of a variable. This is useful in debugging when working with multiple data types. If you think you're adding two numbers, but one is actually a string, the results can be unexpected. Type errors can lurk in calculations or function calls. Especially take care when you're accessing and working with external data in the form of a JavaScript object (JSON).",
+        "You can use <code>typeof</code> to check the data structure, or type, of a variable. This is useful in debugging when working with multiple data types. If you think you're adding two numbers, but one is actually a string, the results can be unexpected. Type errors can lurk in calculations or function calls. Be careful especially when you're accessing and working with external data in the form of a JavaScript Object Notation (JSON) object.",
         "Here are some examples using <code>typeof</code>:",
         "<blockquote>console.log(typeof \"\"); // outputs \"string\"<br>console.log(typeof 0); // outputs \"number\"<br>console.log(typeof []); // outputs \"object\"<br>console.log(typeof {}); // outputs \"object\"</blockquote>",
         "JavaScript recognizes six primitive (immutable) data types: <code>Boolean</code>, <code>Null</code>, <code>Undefined</code>, <code>Number</code>, <code>String</code>, and <code>Symbol</code> (new with ES6) and one type for mutable items: <code>Object</code>. Note that in JavaScript, arrays are technically a type of object.",
