Merge branch 'updateQtInDoc' into 'unstable'

updated developer documentation required libs qt version as it stated we

See merge request !37

Documentation/DeveloperHelpSources/building.docu

@@ -4,12 +4,12 @@
 
 OpenFlipper is developed on top of the Qt framework. This framework provides
 easy cross platform development. Therefore an installed version of QT with
-at least version 4.8.6 is required. We use the cmake MakeFile generator to build 
+at least version 5.5.1 is required. We use the cmake MakeFile generator to build 
 OpenFlipper.
 
 \section reqlibs Required libraries
 <ul>
-<li> 5.5 >= Qt >= 4.8.6  ( http://www.qt.io/download/ ) Use the OpenGL version for Qt >= 5.0</li>
+<li> 5.9 >= Qt >= 5.5.1  ( http://www.qt.io/download/ ) Use the OpenGL version for Qt >= 5.0</li>
 <li> GLUT         ( http://www.opengl.org/resources/libraries/glut/ )</li>
 <li> GLEW (>=1.6) ( http://glew.sourceforge.net )</li>
 </ul>