Update link to Semaphore CI in README
Update link to Semaphore CI in README

Seems the old link for the build status badge that used to work is now broken. It has now been replaced with an updated one. Note that the CI has not changed, just the link to its status.
ScottKolo/UFSMC-Web,ScottKolo/suitesparse-matrix-collection-website,ScottKolo/UFSMC-Web,ScottKolo/suitesparse-matrix-collection-website,ScottKolo/suitesparse-matrix-collection-website,ScottKolo/suitesparse-matrix-collection-website,ScottKolo/UFSMC-Web,ScottKolo/suitesparse-matrix-collection-website