fix: replace .chinese.md extension with .md

curriculum/challenges/chinese/10-coding-interview-prep/project-euler/problem-213-flea-circus.md

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+---
+id: 5900f4411000cf542c50ff54
+challengeType: 5
+title: 'Problem 213: Flea Circus'
+videoUrl: ''
+localeTitle: 问题213：跳蚤马戏团
+---
+
+## Description
+<section id="description">一个30×30的正方形网格包含900个跳蚤，最初是每平方一个跳蚤。当响铃响起时，每个跳蚤随机跳到相邻的广场（通常有4种可能，除了网格边缘或角落处的跳蚤）。 <p>在响铃50次后，预计的未占用方格数量是多少？将您的答案四舍五入到小数点后六位。 </p></section>
+
+## Instructions
+<section id="instructions">
+</section>
+
+## Tests
+<section id='tests'>
+
+```yml
+tests:
+  - text: <code>euler213()</code>应返回330.721154。
+    testString: assert.strictEqual(euler213(), 330.721154);
+
+```
+
+</section>
+
+## Challenge Seed
+<section id='challengeSeed'>
+
+<div id='js-seed'>
+
+```js
+function euler213() {
+  // Good luck!
+  return true;
+}
+
+euler213();
+
+```
+
+</div>
+
+
+
+</section>
+
+## Solution
+<section id='solution'>
+
+```js
+// solution required
+```
+
+/section>