docs/manual: relax python version requirement

Buildroot should now work with host installed python version 3. Update the
manual accordingly.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

docs/manual/prerequisite.txt

@@ -32,7 +32,7 @@ between distributions).
 ** +perl+ (version 5.8.7 or any later)
 ** +tar+
 ** +cpio+
-** +python+ (version 2.6 or 2.7)
+** +python+ (version 2.6 or any later)
 ** +unzip+
 ** +rsync+