Fix link to Sigfox libary reference Related to #1

Author: nicolsc

library.properties

@@ -5,5 +5,5 @@ maintainer=Arduino LLC
 sentence=Helper library for MKRFox1200 board and ATAB8520E Sigfox module
 paragraph=This library allows some high level operations on Sigfox module, to ease integration with existing projects
 category=Device Control
-url=http://arduino.cc/libraries/Sigfox
+url=https://www.arduino.cc/en/Reference/SigFox
 architectures=samd