Update 05_Building_the_Frontend.md

The github issues have been moved to YouTrack and closed on github. The issue is still open, and therefore I changed the URL to the corresponding issue there.

Author: Swissbite

Full Stack Web App with Kotlin Multiplatform/05_Building_the_Frontend.md

@@ -23,7 +23,7 @@ import io.ktor.client.features.json.serializer.KotlinxSerializer
 
 import kotlinx.browser.window
 
-val endpoint = window.location.origin // only needed until https://github.com/ktorio/ktor/issues/1695 is resolved
+val endpoint = window.location.origin // only needed until https://youtrack.jetbrains.com/issue/KTOR-453 is resolved
 
 val jsonClient = HttpClient {
     install(JsonFeature) { serializer = KotlinxSerializer() }