Changed Object type to string type

Author: Athira M

src/main/java/com/google/firebase/remoteconfig/ConditionEvaluator.java

@@ -150,7 +150,7 @@ private boolean evaluateCustomSignalCondition(CustomSignalCondition condition,
       return false;
     }
 
-    Object customSignalValue = context.get(customSignalKey);
+    String customSignalValue = context.get(customSignalKey);
     if (customSignalValue == null) {
       return false;
     }