update makefile

mkdir: cannot create directory '/usr/share/doc/i-nex/': Permission denied
make[1]: *** [install] Error 1
make[1]: Leaving directory `/build/buildd/i-nex-0.5.6'
dh_auto_install: make -j1 install DESTDIR=/build/buildd/i-
nex-0.5.6/debian/i-nex AM_UPDATE_INFO_DIR=no returned exit code 2
make: *** [binary-arch] Error 2
dpkg-buildpackage: error: /usr/bin/fakeroot debian/rules binary-arch gave error exit status 2