SSL error

When this plugin is active, I get an error in Google Developer Tools
This is the error:
Mixed Content: The page at ‘https://www.buyatestkit.com/products/10-panel-dip-drug-test-kit/’ was loaded over HTTPS, but requested an insecure stylesheet ‘https://fonts.googleapis.com/css?family=Open+Sans:300italic,400italic,700italic,300,400,700’. This request has been blocked; the content must be served over HTTPS. It appears to relate to frontmenu.css

When I deactivate the plugin the error goes away.

Can you please help.

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