UI: Use Qt::MiddleButton instead of deprecated Qt::MidButton

UI/hotkey-edit.cpp

@@ -101,7 +101,7 @@ void OBSHotkeyEdit::mousePressEvent(QMouseEvent *event)
 	case Qt::MouseButtonMask:
 		return;
 
-	case Qt::MidButton:
+	case Qt::MiddleButton:
 		new_key.key = OBS_KEY_MOUSE3;
 		break;
 

UI/obs-app.cpp

@@ -116,7 +116,7 @@ QObject *CreateShortcutFilter()
 			case Qt::MouseButtonMask:
 				return false;
 
-			case Qt::MidButton:
+			case Qt::MiddleButton:
 				hotkey.key = OBS_KEY_MOUSE3;
 				break;
 

UI/slider-absoluteset-style.cpp

@@ -15,6 +15,6 @@ int SliderAbsoluteSetStyle::styleHint(QStyle::StyleHint hint,
 				      QStyleHintReturn *returnData = 0) const
 {
 	if (hint == QStyle::SH_Slider_AbsoluteSetButtons)
-		return (Qt::LeftButton | Qt::MidButton);
+		return (Qt::LeftButton | Qt::MiddleButton);
 	return QProxyStyle::styleHint(hint, option, widget, returnData);
 }