Fix Swift4 and Swift3 template comment

Created by: marumemomo

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
• Filed the PR against the correct branch: Default: master.
• Copied the technical committee to review the pull request if your PR is targeting a particular programming language.

Description of the PR

Swift4 and Swift3 client has error when examples contentType=*/*

    /**
     - POST /fake/outer/string
     - Test serialization of outer string types
     - examples: [{contentType=*/*, example=null}]
     - parameter body: (body) Input string as post body (optional)
     - returns: RequestBuilder<String> 
     */
    open class func fakeOuterStringSerializeWithRequestBuilder(body: String? = nil) -> RequestBuilder<String> {
        let path = "/fake/outer/string"
        let URLString = PetstoreClientAPI.basePath + path
        let parameters = body?.encodeToJSON()

        let url = URLComponents(string: URLString)

        let requestBuilder: RequestBuilder<String>.Type = PetstoreClientAPI.requestBuilderFactory.getBuilder()

        return requestBuilder.init(method: "POST", URLString: (url?.string ?? URLString), parameters: parameters, isBody: true)
    }

Add Comment ///

    /**
///  - POST /fake/outer/string
///  - Test serialization of outer string types
///  - examples: [{contentType=*/*, example=null}]
///  - parameter body: (body) Input string as post body (optional)
///  - returns: RequestBuilder<String> 
     */
    open class func fakeOuterStringSerializeWithRequestBuilder(body: String? = nil) -> RequestBuilder<String> {
        let path = "/fake/outer/string"
        let URLString = PetstoreClientAPI.basePath + path
        let parameters = body?.encodeToJSON()

        let url = URLComponents(string: URLString)

        let requestBuilder: RequestBuilder<String>.Type = PetstoreClientAPI.requestBuilderFactory.getBuilder()

        return requestBuilder.init(method: "POST", URLString: (url?.string ?? URLString), parameters: parameters, isBody: true)
    }