fix($core): set NODE_ENV before creating app

[kefranabg]

Summary

Fix #1967

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• Bugfix
• Feature
• Code style update
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Other information:

[ulivz]

Could you also help update the dev section? Thanks

[kefranabg]

@ulivz you mean do the same changes for the dev command ? I already checked but NODE_ENV is never assigned to development or dev in the code.

I did not found any part of the code checking if the current mode is development

[ulivz]

@kefranabg Yes, but setting development under dev is the convention of webpack, maybe user would use it.

[meteorlxy]

What about merging #2028 into this PR? @kefranabg

[meteorlxy]

LGTM

[vue-bot]

Hey @kefranabg, thank you for your time and effort spent on this PR, contributions like yours help make Vue better for everyone. Cheers! 💚