Fix argument type for setContextProperty() on non-OSX

I suspect that using "0" here gets the QObject* overload of this
function, instead of the QVariant one. Fixes web display.

src/main.cpp

@@ -244,7 +244,7 @@ int main(int argc, char *argv[])
 #ifdef Q_OS_MAC
     engine->rootContext()->setContextProperty("webMaxHeight", 1080);
 #else
-    engine->rootContext()->setContextProperty("webMaxHeight", 0);
+    engine->rootContext()->setContextProperty("webMaxHeight", 0.0);
 #endif
 
     // the only way to detect if QML parsing fails is to hook to this signal and then see