fix: add a configure env variable to mute minification warning (fix #1548)

[fi3ework]

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PR checklist:

• Added unit tests
• Updated changelog
• Updated docs (either in the description of this PR as markdown, or as separate PR on the gh-pages branch. Please refer to this PR). For new functionality, at least API.md should be updated
• Added typescript typings
• Verified that there is no significant performance drop (npm run perf)

To fix #1548, I add a simple env variable to force mute the warning in this PR. I wonder is it necessary to add it's usage to docs (as it may be rarely used) 😆

[coveralls]

Coverage remained the same at 93.577% when pulling 337b6aa on fi3ework:fix-#1548 into d55c50a on mobxjs:master.