fixing typo

Author: dret

versions/3.0.md

@@ -6,7 +6,7 @@ The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "S
 
 The OpenAPI Specification is licensed under [The Apache License, Version 2.0](http://www.apache.org/licenses/LICENSE-2.0.html).
 
-## Introductions
+## Introduction
 
 The OpenAPI Specification is a project used to describe and document RESTful APIs.