Merge pull request #273 from awl/patch-1

Fixed typo.

Author: heathermiller

overviews/core/_posts/2012-09-20-implicit-classes.md

@@ -47,7 +47,7 @@ Here's an example:
     HI
     HI
 
-For an implicit class to work, its name must be in scope and unambiuous, like any other implicit
+For an implicit class to work, its name must be in scope and unambiguous, like any other implicit
 value or conversion.