prerequisite.txt: Bump python dependency to 2.7

We now require python 2.7+, so update prerequisite.txt to match.

Signed-off-by: Adam Duskett <Aduskett@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.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 any later)
+** +python+ (version 2.7 or any later)
 ** +unzip+
 ** +rsync+
 ** +file+ (must be in +/usr/bin/file+)