Remove -Xopt-in compiler argument

We don't need to opt in to the experimental Time class any longer.

build.gradle

@@ -33,7 +33,6 @@ test {
 def jvmTargetVersion = "11"
 compileKotlin {
     kotlinOptions.jvmTarget = jvmTargetVersion
-    kotlinOptions.freeCompilerArgs += "-Xopt-in=kotlin.RequiresOptIn"
 }
 compileJava {
     targetCompatibility = jvmTargetVersion

src/main/kotlin/org/mosad/thecitadelofricks/controller/CacheController.kt

@@ -255,7 +255,6 @@ class CacheController {
          * update the CourseList every 24h, the Timetables every 3h and the Mensa Menu every hour
          * doesn't account the change between winter and summer time!
          */
-        @OptIn(ExperimentalTime::class)
         private fun scheduledUpdates() {
             val currentTime = System.currentTimeMillis()