Updated a type signature

server/db/database.ts

@@ -24,11 +24,9 @@ function once<T extends (...args: any) => any>(fn: T, message: string): T {
     }) as T
 }
 
-interface Lock {
+type Lock = () => void
-    (): void
-}
 
-interface Mutex {
+type Mutex = {
     lock(): Promise<Lock>
 }