[DOC] inline help typos

[ubidefeo]

while happily typing through the help I found this when invoking arduino-cli core download -h:
spaces are missing in the inline help

Examples:
  arduino-clicore download arduino:samd       # to download the latest version of arduino SAMD core.
  arduino-clicore download arduino:samd=1.6.9 # for a specific version (in this case 1.6.9).