fix #154 - _fingerprint not declared in this scope

fix #154 - _fingerprint not declared in this scope

src/WebSocketsClient.cpp

@@ -40,8 +40,10 @@ WebSocketsClient::~WebSocketsClient() {
 void WebSocketsClient::begin(const char *host, uint16_t port, const char * url) {
     _host = host;
     _port = port;
+#if (WEBSOCKETS_NETWORK_TYPE == NETWORK_ESP8266)
     _fingerprint = "";
-
+#endif
+    
     _client.num = 0;
     _client.status = WSC_NOT_CONNECTED;
     _client.tcp = NULL;