Update README.md (cvat-ai#1040)

Author: bsekachev

README.md

@@ -4,7 +4,6 @@
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-[![Maintainability](https://api.codeclimate.com/v1/badges/0461727199dfe049b2f1/maintainability)](https://codeclimate.com/github/opencv/cvat/maintainability)
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