fix: replace .english.md extension with .md

curriculum/challenges/english/10-coding-interview-prep/rosetta-code/leap-year.md

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+---
+id: 5a23c84252665b21eecc7ede
+title: Leap year
+challengeType: 5
+forumTopicId: 302300
+---
+
+## Description
+
+<section id='description'>
+
+Determine whether a given year is a leap year in the Gregorian calendar.
+
+</section>
+
+## Instructions
+
+<section id='instructions'>
+
+</section>
+
+## Tests
+
+<section id='tests'>
+
+```yml
+tests:
+  - text: <code>isLeapYear</code> should be a function.
+    testString: assert(typeof isLeapYear == 'function');
+  - text: <code>isLeapYear()</code> should return a boolean.
+    testString: assert(typeof isLeapYear(2018) == 'boolean');
+  - text: <code>isLeapYear(2018)</code> should return <code>false</code>.
+    testString: assert.equal(isLeapYear(2018), false);
+  - text: <code>isLeapYear(2016)</code> should return <code>true</code>.
+    testString: assert.equal(isLeapYear(2016), true);
+  - text: <code>isLeapYear(2000)</code> should return <code>true</code>.
+    testString: assert.equal(isLeapYear(2000), true);
+  - text: <code>isLeapYear(1900)</code> should return <code>false</code>.
+    testString: assert.equal(isLeapYear(1900), false);
+  - text: <code>isLeapYear(1996)</code> should return <code>true</code>.
+    testString: assert.equal(isLeapYear(1996), true);
+  - text: <code>isLeapYear(1800)</code> should return <code>false</code>.
+    testString: assert.equal(isLeapYear(1800), false);
+```
+
+</section>
+
+## Challenge Seed
+
+<section id='challengeSeed'>
+
+<div id='js-seed'>
+
+```js
+function isLeapYear(year) {
+
+}
+```
+
+</div>
+</section>
+
+## Solution
+
+<section id='solution'>
+
+```js
+function isLeapYear(year) {
+  return year % 100 === 0 ? year % 400 === 0 : year % 4 === 0;
+}
+```
+
+</section>