Fix build on FreeBSD again
Fix build on FreeBSD again

json_ui.cc:29:9: error: use of undeclared identifier 'sprintf'
        sprintf(buffer, R"("#%02x%02x%02x")", color.r, color.g, color.b);
        ^
1 error generated.

Regressed by 7cdbe1d3d24c1cc13bd7cbc3fe252f1e88747ffb

casimir/kakoune,jkonecny12/kakoune,Somasis/kakoune,Somasis/kakoune,occivink/kakoune,Somasis/kakoune,casimir/kakoune,jkonecny12/kakoune,alexherbo2/kakoune,Somasis/kakoune,lenormf/kakoune,casimir/kakoune,occivink/kakoune,occivink/kakoune,mawww/kakoune,danr/kakoune,mawww/kakoune,lenormf/kakoune,alexherbo2/kakoune,jkonecny12/kakoune,danr/kakoune,alexherbo2/kakoune,casimir/kakoune,lenormf/kakoune,jkonecny12/kakoune,mawww/kakoune,lenormf/kakoune,alexherbo2/kakoune,occivink/kakoune,mawww/kakoune,danr/kakoune,danr/kakoune