Make schema example property spec compliant

According to the official specification (https://github.com/OAI/OpenAPI-Specification/blob/master/versions/2.0.md), the example property of the Schema object should not have any type requirements and should therefore be any.

types/swagger-schema-official/index.d.ts

@@ -147,7 +147,7 @@ export interface Schema extends BaseSchema {
   readOnly?: boolean;
   xml?: XML;
   externalDocs?: ExternalDocs;
-  example?: {[exampleName: string]: {}};
+  example?: any;
   required?: string[];
 }