Bump version to 3.4.0

Author: esphomebot

library.json

@@ -12,7 +12,7 @@
     "type": "git",
     "url": "https://github.com/esphome/ESPAsyncWebServer.git"
   },
-  "version": "3.3.1",
+  "version": "3.4.0",
   "license": "LGPL-3.0",
   "frameworks": "arduino",
   "platforms": ["espressif8266", "espressif32", "libretiny"],