Sigfox library documentation error: SigFox.endPacket

The documentation on the SigFox library for the _endPacket()_ function contains an error. It says:
"Returns an int: 1 if the packet was sent successfully, 0 if there was an error"

while the example code says ( and is correct):
```c++
if (ret == 0)
Serial.println("OK");
else
Serial.println("KO");
```
URL: https://www.arduino.cc/en/Reference/SigFoxEndPacket

Open the SigFox endPacket reference page at the URL and compare its return-value description with the example code. Correct the prose so it matches the example's documented success and error values, then verify the page no longer contradicts the example.

Written by the indexing model from the issue text.