Update FLTK requirement
We actually require FLTK 1.3.2 as we reference FL_SOCKET.
diff --git a/BUILDING.txt b/BUILDING.txt
index 98c7c6b..f5944d7 100644
--- a/BUILDING.txt
+++ b/BUILDING.txt
@@ -84,8 +84,8 @@
Building FLTK
=============
-TigerVNC requires FLTK 1.3.0 (or later). Although it will build and work
-with plain 1.3.0, to get full functionality and the best behaviour you
+TigerVNC requires FLTK 1.3.2 (or later). Although it will build and work
+with plain 1.3.2, to get full functionality and the best behaviour you
need to build a patched version:
1. Check out FLTK 1.3.2 using Subversion: