updating installation docs

Signed-off-by: Joshua Ferraro <jmf@liblime.com>

INSTALL.debian

@@ -72,7 +72,7 @@ Note: for more information about Git, please see the Koha Git Usage Guide:
 
 1.4.2 Option B: Download Koha from http://download.koha.org
 
-    $ wget http://download.koha.org/koha-3.00.00-alpha.tar.gz
+    $ wget http://download.koha.org/koha-3.00.00-beta.tar.gz
     ( Note: use the latest stable version)
 
 1.5 Install additional Debian dependencies