find_chrome() can't find Chromium on Mac

[rossellhayes]

find_chrome() currently only looks for Chromium on Linux. On Mac and Windows, it only looks for Google Chrome.

I can't speak to Windows, but Chromium support could be added on Mac by tweaking the logic in #13, because Sys.which("chromium") works on Mac (at least if Chromium is installed through Homebrew).

if (is_mac()) {
  path <- "/Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome"
  if (!file.exists(path)) {
    path <- Sys.which("chromium-browser")
  }
  if (nchar(path) == 0) {
    path <- Sys.which("chromium")
  }
  if (nchar(path) == 0) {
    message("Google Chrome and Chromium were not found. Try setting the `CHROMOTE_CHROME` environment variable.")
    path <- NULL
  }
}

I'd be happy to open a PR if this would be appreciated!

[gadenbuie]

Thanks @rossellhayes! This should be addressed by #117 (we now try the linux options on Mac, just in case).