base64 decode - lower case

[mnimm]

"base64 -D" should be "base64 -d" (at least with base64 from GNU coreutils). Results in "base64: invalid option -- 'D'" otherwise.

[agolzer]

Darwin (macOS) needs uppercase "-D" while Linux needs a lowercase "-d". I created an alternate PR #4

[georgettica]

yup, I can vouch for a +1 for @agolzer's request