use out of resources when execute hexo generate

[sfantree]

test environment

• win7 & ubuntu16.04
• nodejs 8.9.3
• npm 5.6.0(cnpm 5.1.1)
• hexo-cli: 1.0.4

That it use out of resources leads to collapse after I execute hexo generate, i think it downloads too many files in theme directory after execute npm install , but hexo will traverse all the files include node_modules under the theme directory