fixed a variable substitution

Author: darrelmiller

versions/3.0.md

@@ -1808,7 +1808,7 @@ This object can be extended with [Specification Extensions](#specificationExtens
 
 The key used to identify the [Path Item Object](#pathItemObject) is a variable expression that can be evaluated in the context of a runtime HTTP request/response to identify the URL to be used for the callback request.
 A simple example might be `$request.body#/url`.
-However, using a [variable substitution](#runtimeExpression) syntax the complete HTTP message can be accessed.
+However, using a [runtime expression](#runtimeExpression) the complete HTTP message can be accessed.
 This includes accessing any part of a body that can be accessed using a JSON Pointer [RFC6901](https://tools.ietf.org/html/rfc6901). 
 
 For example, given the following HTTP request: