Bump version number (#50)

* Null check for _savecallback

* Bump version number

library.json

@@ -9,5 +9,5 @@
   },
   "frameworks": "arduino",
   "platforms": ["espressif8266", "espressif32"],
-  "version": "0.19"
+  "version": "0.20"
 }

library.properties

@@ -1,5 +1,5 @@
 name=ESP Async WiFi Manager
-version=0.19
+version=0.20
 author=alanswx
 maintainer=alanswx
 sentence=ESP8266 and ESP32 Async WiFi Connection manager with fallback web configuration portal