Use node_js: 8 on Travis
Use node_js: 8 on Travis

k0kubun/githubranking,k0kubun/githubranking,k0kubun/github-ranking,k0kubun/github-ranking,k0kubun/githubranking,k0kubun/github-ranking,k0kubun/githubranking,k0kubun/githubranking,k0kubun/github-ranking,k0kubun/github-ranking