README.md: update browser logo urls
README.md: update browser logo urls

They were broken by
https://github.com/alrra/browser-logos/commit/a335e3357a524160c33e9b0c33b72f7d57d58c6e#diff-1d435e808f4e1e3adde9ff9ff27acce9

josephfrazier/browser-extension,josephfrazier/browser-extension,OctoLinker/browser-extension,josephfrazier/browser-extension,OctoLinker/browser-extension,OctoLinker/browser-extension