fix(bin/linja): which does not look for 'sbin'
fix(bin/linja): which does not look for 'sbin'

Ubuntu-12/14 has two packages which provide a binary file `ninja`:

 1. ninja : http://forkbomb.org/ninja/
 2. ninja-build : http://martine.github.io/ninja/

We had a case where a user has ninja installed instead of ninja-build,
then linja confuses that it has ninja-build and tries to use it.

This commit excludes a directory whose name includes "sbin" in finding a
system program. As a result, `which` will not find ninja[1] which
resides at /usr/sbin.

fpvandoorn/lean,digama0/lean,Kha/lean,fpvandoorn/lean2,dselsam/lean,soonhokong/lean,eigengrau/lean,leodemoura/lean,htzh/lean,levnach/lean,avigad/lean,johoelzl/lean,fpvandoorn/lean,eigengrau/lean,avigad/lean,fgdorais/lean,dselsam/lean,soonhokong/lean-osx,Kha/lean,eigengrau/lean,fgdorais/lean,eigengrau/lean,sp3ctum/lean,sp3ctum/lean,leodemoura/lean,rlewis1988/lean,leanprover-community/lean,dselsam/lean,soonhokong/lean-osx,johoelzl/lean,UlrikBuchholtz/lean,fgdorais/lean,digama0/lean,leanprover-community/lean,fgdorais/lean,avigad/lean,avigad/lean,soonhokong/lean-osx,johoelzl/lean,leodemoura/lean,johoelzl/lean,levnach/lean,javra/lean,UlrikBuchholtz/lean,fpvandoorn/lean,rlewis1988/lean,avigad/lean,leanprover/lean,levnach/lean,fgdorais/lean,johoelzl/lean,digama0/lean,javra/lean,fpvandoorn/lean,avigad/lean,soonhokong/lean-windows,digama0/lean,c-cube/lean,Kha/lean,javra/lean,leanprover-community/lean,leodemoura/lean,c-cube/lean,htzh/lean,rlewis1988/lean,c-cube/lean,fpvandoorn/lean2,soonhokong/lean-windows,leanprover/lean,Kha/lean,htzh/lean,rlewis1988/lean,fpvandoorn/lean,soonhokong/lean,rlewis1988/lean,javra/lean,levnach/lean,dselsam/lean,leanprover-community/lean,htzh/lean,sp3ctum/lean,fpvandoorn/lean2,dselsam/lean,leanprover/lean,digama0/lean,fgdorais/lean,Kha/lean,soonhokong/lean-windows,leanprover-community/lean,c-cube/lean,leanprover-community/lean,johoelzl/lean,soonhokong/lean-osx,eigengrau/lean,UlrikBuchholtz/lean,leanprover/lean,UlrikBuchholtz/lean,levnach/lean,digama0/lean,soonhokong/lean-windows,fpvandoorn/lean2,leanprover/lean,sp3ctum/lean,rlewis1988/lean,UlrikBuchholtz/lean,leodemoura/lean,soonhokong/lean,c-cube/lean,fpvandoorn/lean,Kha/lean,javra/lean,dselsam/lean,soonhokong/lean,fpvandoorn/lean2,htzh/lean,soonhokong/lean-windows,soonhokong/lean-osx,leanprover/lean,leodemoura/lean,sp3ctum/lean,soonhokong/lean