bin-src.cabal - relax requirements for GHC 7.6.3

GHC 7.6.3 makes use of base 4.6 instead of 4.5 and directory 1.2 instead
of 1.1 . The changes in this patch relax the version requirements of
these two packages so that we can properly set up bin-src on a machine
with GHC 7.6.3

Signed-off-by: Pang Yan Han <pangyanhan@gmail.com>