pushString does not work

[alpellegri]

Hi guys,

please change:
String FirebaseArduino::pushString(const String& path, const String& value) {
JsonVariant json(value);
return push(path, json);
}

into:
String FirebaseArduino::pushString(const String& path, const String& value) {
JsonVariant json(value.c_str());
return push(path, json);
}