Use Class<?> in WorkManager#tryCreateFirebaseJobScheduler

This allows for compiler generic type check and, most importantly,
removes the IDE linting error

Test: Ran existing tests
Change-Id: I48e9e7fc37b31bfc805f0c30d9886c9c120e0bbb
diff --git a/background/workmanager/src/main/java/android/arch/background/workmanager/WorkManager.java b/background/workmanager/src/main/java/android/arch/background/workmanager/WorkManager.java
index 23f8734..4e986ea 100644
--- a/background/workmanager/src/main/java/android/arch/background/workmanager/WorkManager.java
+++ b/background/workmanager/src/main/java/android/arch/background/workmanager/WorkManager.java
@@ -86,7 +86,7 @@
     private Scheduler tryCreateFirebaseJobScheduler(Context context) {
         Scheduler scheduler = null;
         try {
-            Class firebaseSchedulerClass = Class.forName(FIREBASE_SCHEDULER_CLASSNAME);
+            Class<?> firebaseSchedulerClass = Class.forName(FIREBASE_SCHEDULER_CLASSNAME);
             scheduler = (Scheduler) firebaseSchedulerClass
                     .getConstructor(Context.class)
                     .newInstance(context);