Wrong converting from .otf to .ttf, glyphs become transparent!
I discovered this issue when converting `Gilroy-Light.otf` to `.ttf` format with your plugin `otf2ttf`, in Windows it displays wrong and all glyphs are transparent, but the same file on Mac displays correctly, i don't know what the problem on Windows. Hence, `.woff` and `.woff2` files on Windows also trasparent. You may check `.otf`, `.ttf` and `.woff` glyphs in browser via https://fontdrop.info/.

This font with free license by Radomir Tinkov, you may download and check it - https://www.tinkov.info/gilroy.html
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![otf](https://user-images.githubusercontent.com/22091732/64271166-8904d880-cf45-11e9-9c88-81ac3c385dee.jpg)
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After converting:
![ttf](https://user-images.githubusercontent.com/22091732/64271167-8904d880-cf45-11e9-93db-dc11006cf8c0.jpg)