[skip CI] [Gui] NaviCube.cpp revert a change

from commit cb5e316a708f since the intended fix is not universal for all cube sizes, therefore leave the old pen width as compromise that obviously worked well

(as strange as it is, restarting FC brings me everytime a different border width)

src/Gui/NaviCube.cpp

@@ -368,7 +368,7 @@ GLuint NaviCubeImplementation::createCubeFaceTex(QtGLWidget* gl, float gap, cons
 	QImage image(texSize, texSize, QImage::Format_ARGB32);
 	image.fill(qRgba(255, 255, 255, 0));
 	QPainter paint;
-	QPen pen(Qt::black, 6 * m_BorderWidth);
+	QPen pen(Qt::black, 10);
 	paint.begin(&image);
 	paint.setRenderHints(QPainter::Antialiasing | QPainter::TextAntialiasing | QPainter::SmoothPixmapTransform);