Set global mapping to be global static

bubble-server/src/main/java/bubble/cloud/storage/StorageServiceDriverBase.java

@@ -20,7 +20,7 @@ import static org.cobbzilla.util.security.ShaUtil.sha256_hex;
 
 public abstract class StorageServiceDriverBase<T> extends CloudServiceDriverBase<T> implements StorageServiceDriver {
 
-    private final Map<String, WriteRequest> requestMap = new ConcurrentHashMap<>();
+    private static final Map<String, WriteRequest> requestMap = new ConcurrentHashMap<>();
 
     private static final Map<String, WriteRequestCleaner> cleaners = new ConcurrentHashMap<>();