Set up gulp-eslint to check JavaScript by Git pre-commit hook (using pre-commit package.)

我其實.. 也不知道當初為什麼要用英文寫，而且寫得蠻爛的，但我自己看得懂啦，應該是早上上班寫 code 很急，我也不想花太多時間整理了...

If we can't control other developers, but we can control some commit rule for other developer. that's why i want to use pre-commit, it can help to check other developer code convention.

By Using gulp-eslint and pre-commit.
Because my project is fully frontend project. so... i use gulp-eslint replace with eslint.

Step summary:
1. install gulp-eslint
2. install pre-commit
3. create you eslint config file, there are serveral format for eslint config file, you can go here.