fix: http://cnpmjs.org/package/fms pre style

[nimoc]

http://cnpmjs.org/package/fms
自动生成数据文档章节的 pre 标签 color 值使用了 main.css 的 color: #fff;

[codecov-io]

Current coverage is 89.05%

Merging #739 into master will increase coverage by +0.03% as of 40a0d3d

@@            master    #739   diff @@
======================================
  Files           84      84       
  Stmts         3180    3180       
  Branches         0       0       
  Methods          0       0       
======================================
+ Hit           2831    2832     +1
  Partial          0       0       
+ Missed         349     348     -1

Review entire Coverage Diff as of 40a0d3d

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[alsotang]

可以截图看看对比效果吗？

[fengmk2]

before

afater