Config baseDir support array

[whu12yz]

Checklist

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

Affected core subsystem(s)

Affect baseDir config!

Description of change

Config options baseDir support directory array, And also compatible with string!
example:

exports.sequelize = {
   baseDir: ['model', 'other-model'], // load all files in `app/${baseDir}` as models, default to `model`
};

[codecov]

Codecov Report

Merging #89 (33816cb) into master (f585da5) will increase coverage by 0.43%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #89      +/-   ##
==========================================
+ Coverage   85.71%   86.15%   +0.43%     
==========================================
  Files           4        4              
  Lines          63       65       +2     
==========================================
+ Hits           54       56       +2     
  Misses          9        9              

Impacted Files	Coverage Δ
lib/loader.js	85.00% <100.00%> (+0.51%)	⬆️

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[whu12yz]

travis-ci npm install error cause of index.d.ts change?