Popover arrow has wrong style in prod mode

[denStrigo]

Issue type

I'm submitting a ... (check one with "x")

• bug report
• feature request

Issue description

Current behavior:
Popover array has wrong style in prod mode.

Expected behavior:
Should be:

Steps to reproduce:
Buld peoject in prod mode

Related code:

insert short code snippets here

Other information:

npm, node, OS, Browser

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Angular, Nebular

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[yggg]

Caused by clean-css/clean-css#1053