Fix typo.

Author: dwillmer

docs/classes.md

@@ -114,7 +114,7 @@ class Something {
 
 var s1 = new Something();
 var s2 = new Something();
-console.log(Someting.instances); // 2
+console.log(Something.instances); // 2
 ```
 
 You can have static members as well as static functions.