Bump to C++17 in xdf.pro (#44)

* Bump to C++20 in xdf.pro

* Change to C++17 instead

Author: Yida-Lin

xdf.pro

@@ -2,7 +2,7 @@ QT -= gui
 
 TARGET = xdf
 TEMPLATE = lib
-CONFIG += c++11 shared_and_static build_all
+CONFIG += c++17 shared_and_static build_all
 INCLUDEPATH += pugixml
 
 QMAKE_CFLAGS += -std=c99