Update to the Crossref icon?
Hi - could I request an update to the Crossref icon to fit our style guide? There is a single colour (full) logo attached that perhaps you could take the icon from, or I can ask a designer if needed? Many thanks for this work - it's much appreciated! 
[crossref-singlecolour-logo.zip](https://github.com/jpswalsh/academicons/files/6147579/crossref-singlecolour-logo.zip)
