URL fixed. Was broken & linking to deleted page.

Change-Id: Iefe842aa8ef3b183b90f896902edd8941fb1b238
Reviewed-on: https://gerrit.libreoffice.org/63967Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
Tested-by: Stephan Bergmann <sbergman@redhat.com>

solenv/gbuild/README

@@ -2,7 +2,7 @@
 GBuild is a set of makefile macros built on top of gmake that attempts to simplify LibreOffice development.
 
 See
-  https://wiki.documentfoundation.org/Development/Build_System/
+  https://wiki.documentfoundation.org/Development/Build_System
 for online build-system documentation.
 
 See