fix: mem fs bugs in windows

[whxaxes]

Checklist

• npm test passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

Description of change

修复 egg-init 在 windows 下由于 mem-fs 带来的卡死问题，发现引入 mem-fs 没多大意义，不如直接落盘，因此改成直接落盘。

[codecov]

Codecov Report

Merging #48 into master will increase coverage by 0.2%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master      #48     +/-   ##
=========================================
+ Coverage   85.36%   85.57%   +0.2%     
=========================================
  Files           1        1             
  Lines         205      201      -4     
=========================================
- Hits          175      172      -3     
+ Misses         30       29      -1

Impacted Files	Coverage Δ
lib/init_command.js	85.57% <100%> (+0.2%)	⬆️

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[codecov]

Codecov Report

Merging #48 into master will decrease coverage by 0.29%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master      #48     +/-   ##
=========================================
- Coverage   85.36%   85.07%   -0.3%     
=========================================
  Files           1        1             
  Lines         205      201      -4     
=========================================
- Hits          175      171      -4     
  Misses         30       30

Impacted Files	Coverage Δ
lib/init_command.js	85.07% <100%> (-0.3%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 0704648...cb3a8a4. Read the comment docs.

[whxaxes]

@atian25 我好像没有这个包的权限，你发一下？或者给我加一下权限

$ npm owner add wanghx egg-init

[whxaxes]

1.5.1

[rojer95]

1.15.1版本依旧卡死额.

系统window10...

另外
egg-init --type sequelize schat-server 这样不会卡死
egg-init schat-server 这样会卡死

[whxaxes]

@rojer95 我晚上回去用 windows 试一下，现在身边没有 windows 机器

[bi-kai]

@whxaxes
现在创建项目是用egg-init还是npm init egg --type=simple?
后者只是创建了一个普通package.json：

[atian25]

升级你的 npm 版本，至少是 5.10+