Bump ESPAsyncWebserver version

Without this patch, the build fails with:
PackageException: Package version 2.1.0+sha.6bf93e9 doesn't satisfy requirements ~2.0.7 based on PackageMetadata <type=library name=ESPAsyncWebServerWLED version=2.1.0+sha.6bf93e9 spec={'owner': None, 'id': None, 'name': 'ESPAsyncWebServer', 'requirements': '~2.0.7', 'uri': 'git+https://github.com/Aircoookie/ESPAsyncWebServer.git'}

Signed-off-by: Alastair D'Silva <alastair@d-silva.org>

platformio.ini

@@ -144,7 +144,7 @@ lib_deps =
     fastled/FastLED @ 3.6.0
     IRremoteESP8266 @ 2.8.2
     Makuna/NeoPixelBus @ 2.7.8
-    https://github.com/Aircoookie/ESPAsyncWebServer.git @ ~2.0.7
+    https://github.com/Aircoookie/ESPAsyncWebServer.git @ ~2.1.0
   # for I2C interface
     ;Wire
   # ESP-NOW library