Fix 'obj[type]' const char*

[ig0rb]

it was declared char and not const char...

Error I had.. .pio/libdeps/esp01/WebConfig/src/WebConfig.cpp:148:38: required from here .pio/libdeps/esp01/ArduinoJson/src/ArduinoJson/Variant/VariantRefBase.hpp:95:7: error: no type named 'type' in 'struct ArduinoJson6200_F1::enable_if<false, bool>' .pio/libdeps/esp01/ArduinoJson/src/ArduinoJson/Variant/VariantRefBase.hpp:106:3: note: candidate: 'template<class T> typename ArduinoJson6200_F1::enable_if<(((! ArduinoJson6200_F1::ConverterNeedsWriteableRef<T>::value) && (! ArduinoJson6200_F1::is_same<T, char*>::value)) && (! ArduinoJson6200_F1::is_same<T, char>::value)), bool>::type ArduinoJson6200_F1::VariantRefBase<TDerived>::is() const [with T = T; TDerived = ArduinoJson6200_F1::MemberProxy<ArduinoJson6200_F1::JsonObject, const char*>]'