CONTRIBUTING.md: minor URL cleanups
CONTRIBUTING.md: minor URL cleanups

use `https://` and `.svg`, follow a redirect.
thejameskyle/linguist,erkyrath/linguist,tschf/linguist,pchaigno/linguist,R4PaSs/linguist,hcatlin/linguist,yscho/linguist,BerkeleyTrue/linguist,ppaulweber/github-linguist,pcantrell/linguist,ilyes14/linguist,sebgod/linguist,steventhanna/linguist,georgesuperman/linguist,georgesuperman/linguist,mwpastore/linguist,MahmoudFayed/linguist,kr/linguist,tschf/linguist,adamkaplan/linguist,seanders/linguist,PsichiX/linguist,stanhu/linguist,JJ/linguist,matt40k/linguist,PsichiX/linguist,MadcapJake/linguist,stanhu/linguist,manveru/linguist,CoderXpert/linguist,BerkeleyTrue/linguist,hcutler/linguist,cokeboL/linguist,kyoungrok0517/linguist,bluebear94/linguist,github/linguist,a0viedo/linguist,adamkaplan/linguist,sebgod/linguist,yyx990803/linguist,ya7lelkom/linguist,meunierfrederic/octocatlinguist,JJ/linguist,MostAwesomeDude/linguist,R4PaSs/linguist,pchaigno/linguist,a0viedo/linguist,pchaigno/linguist,scttnlsn/linguist,scttnlsn/linguist,chiranjeevjain/linguist,seanders/linguist,yscho/linguist,Mx7f/linguist,whitj00/linguist,osorgin/linguist,sebgod/linguist,nburkley/linguist,steventhanna/linguist,stanhu/linguist,jtbandes/linguist,martynbm/linguist,Mx7f/linguist,jrnold/linguist,sagar290/linguist,MahmoudFayed/linguist,nburkley/linguist,christop/linguist,meunierfrederic/octocatlinguist,github/linguist,assimovt/ling-ist,douglas-larocca/linguist,cokeboL/linguist,MostAwesomeDude/linguist,c-lipka/linguist,FStarLang/linguist,ammaraskar/linguist,assimovt/ling-ist,hcatlin/linguist,yyx990803/linguist,chiranjeevjain/linguist,ilyes14/linguist,stanhu/linguist,kr/linguist,bluebear94/linguist,jtbandes/linguist,alitalia/linguist,davidzchen/linguist,pcantrell/linguist,iblech/linguist,douglas-larocca/linguist,github/linguist,osorgin/linguist,JJ/linguist,matt40k/linguist,jjatria/linguist,c-lipka/linguist,ammaraskar/linguist,erkyrath/linguist,phpsgi/linguist,alitalia/linguist,sebgod/linguist,CoderXpert/linguist,phpsgi/linguist,CegepVictoriaville/linguist,jrnold/linguist,JJ/linguist,martynbm/linguist,github/linguist,thejameskyle/linguist,cybernet14/linguist,erkyrath/linguist,manveru/linguist,sagar290/linguist,yyx990803/linguist,whitj00/linguist,hcutler/linguist,erkyrath/linguist,FStarLang/linguist,cybernet14/linguist,mwpastore/linguist,ppaulweber/github-linguist,christop/linguist,pchaigno/linguist,CegepVictoriaville/linguist,davidzchen/linguist,MadcapJake/linguist,jjatria/linguist,kyoungrok0517/linguist,iblech/linguist,yyx990803/linguist,ya7lelkom/linguist,meunierfrederic/octocatlinguist