fix a broken link
fix a broken link

ee3aa831172090fd5442820f215cb04ab6062756 added a broken link
which results in 404. The broken part is reference to a
nonexistent file "CheatSheet.md" instead of "cheet_sheet.md".

antidotcb/googletest,jlanecox/googletest,jlanecox/googletest,gianricardo/googletest,jlanecox/googletest,google/googletest,google/googletest,antidotcb/googletest,jlanecox/googletest,empiredan/googletest,google/googletest,antidotcb/googletest,gianricardo/googletest,empiredan/googletest,gianricardo/googletest,google/googletest,empiredan/googletest,antidotcb/googletest