Sync the leap exercise's docs with the latest data. (#2362)

exercises/practice/leap/.docs/introduction.md

@@ -2,15 +2,15 @@
 
 A leap year (in the Gregorian calendar) occurs:
 
-- In every year that is evenly divisible by 4
+- In every year that is evenly divisible by 4.
 - Unless the year is evenly divisible by 100, in which case it's only a leap year if the year is also evenly divisible by 400.
 
 Some examples:
 
 - 1997 was not a leap year as it's not divisible by 4.
-- 1900 was not a leap year as it's not divisible by 400
+- 1900 was not a leap year as it's not divisible by 400.
 - 2000 was a leap year!
 
-```exercism/note
-For a delightful, four minute explanation of the whole phenomenon of leap years, check out [this youtube video](https://www.youtube.com/watch?v=xX96xng7sAE).
-```
+~~~~exercism/note
+For a delightful, four-minute explanation of the whole phenomenon of leap years, check out [this YouTube video](https://www.youtube.com/watch?v=xX96xng7sAE).
+~~~~