Fix nullability of Menu in onCreateOptionsMenu

... override of LoadingActivity and StaggerActivity.

The parameter should be non null, but the current override type is Menu?

Author: srmurguia

Motion/app/src/main/java/com/example/android/motion/demo/loading/LoadingActivity.kt

@@ -87,7 +87,7 @@ class LoadingActivity : AppCompatActivity() {
         }
     }
 
-    override fun onCreateOptionsMenu(menu: Menu?): Boolean {
+    override fun onCreateOptionsMenu(menu: Menu): Boolean {
         menuInflater.inflate(R.menu.loading, menu)
         return super.onCreateOptionsMenu(menu)
     }

Motion/app/src/main/java/com/example/android/motion/demo/stagger/StaggerActivity.kt

@@ -77,7 +77,7 @@ class StaggerActivity : AppCompatActivity() {
         }
     }
 
-    override fun onCreateOptionsMenu(menu: Menu?): Boolean {
+    override fun onCreateOptionsMenu(menu: Menu): Boolean {
         menuInflater.inflate(R.menu.stagger, menu)
         return super.onCreateOptionsMenu(menu)
     }