docs(error/$compile:tplrt): fix typo

Closes #13992

Author: martinsik

docs/content/error/$compile/tplrt.ngdoc

@@ -31,7 +31,7 @@ single root element, like the `div` element in this template:
 <div><b>Hello</b> World!</div>
 ```
 
-An an invalid template to be used with this directive is one that defines multiple root nodes or
+An invalid template to be used with this directive is one that defines multiple root nodes or
 elements. For example:
 
 ```