fix git command

Author: jmckenna

en/introduction.txt

@@ -987,5 +987,5 @@ configuration, basic MapServer topics and features, incorporation of
 dynamic data, advanced topics, MapScript, and the creation of an
 actual application.
 
-.. _`MapServer issue tracker`: http://github.com/MapServer/MapServer/issues
+.. _`MapServer issue tracker`: https://github.com/MapServer/MapServer/issues
 .. _`MapServer documentation issue tracker`: https://github.com/MapServer/MapServer-documentation/issues