Add type declarations for the methods writeValueWithoutResponse and…

… `writeValueWithResponse` (#63)

* add type declarations for `writeValueWithoutResponse` and `writeValueWithResponse` methods

Add type declarations for the methods `writeValueWithoutResponse` and `writeValueWithResponse` that were added to `GattCharacteristic` with #47

* Fix typo

src/index.d.ts

@@ -7,6 +7,8 @@ declare namespace NodeBle {
         isNotifying(): Promise<boolean>;
         readValue(offset?: number): Promise<Buffer>;
         writeValue(buffer: Buffer, optionsOrOffset?: number | WriteValueOptions): Promise<void>;
+        writeValueWithoutResponse(buffer: Buffer, offset?: number): Promise<void>;
+        writeValueWithResponse(buffer: Buffer, offset?: number): Promise<void>;
         startNotifications(): Promise<void>;
         stopNotifications(): Promise<void>;
         toString(): Promise<string>;