fix(migration): always use production config

[zhangjx]

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

Environment

Node: v6.9.0
egg-sequelize: 2.1.3

Description

When use npm run migrate:up always error, because the config file is covered by the production environment. See #895

[mention-bot]

@zhangjx, thanks for your PR! By analyzing the history of the files in this pull request, we identified @huacnlee to be a potential reviewer.

[codecov]

Codecov Report

Merging #14 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master    #14   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           5      5           
  Lines          36     36           
=====================================
  Hits           36     36

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[popomore]

• egg-sequelize@2.1.4