[fix] install npm packages locally on .travis.yml
[fix] install npm packages locally on .travis.yml

for some reason installing grunt globally caused travis test to fail.

dalf/searx,misnyo/searx,PwnArt1st/searx,jcherqui/searx,jibe-b/searx,potato/searx,matejc/searx,jcherqui/searx,potato/searx,pointhi/searx,jcherqui/searx,potato/searx,matejc/searx,jibe-b/searx,jibe-b/searx,asciimoo/searx,pointhi/searx,pointhi/searx,matejc/searx,asciimoo/searx,PwnArt1st/searx,misnyo/searx,misnyo/searx,pointhi/searx,asciimoo/searx,PwnArt1st/searx,dalf/searx,jcherqui/searx,jibe-b/searx,matejc/searx,potato/searx,dalf/searx,asciimoo/searx,dalf/searx,misnyo/searx,PwnArt1st/searx