Don't error when nothing to do

[jdonaghue]

issue #95

• Do not throw error when nothing to do
• When no commands have eject method, message that there is nothing to do

[codecov-io]

Codecov Report

Merging #99 into master will increase coverage by 0.03%.

@@            Coverage Diff             @@
##           master      #99      +/-   ##
==========================================
+ Coverage   99.45%   99.49%   +0.03%     
==========================================
  Files          15       15              
  Lines         368      394      +26     
  Branches       43       49       +6     
==========================================
+ Hits          366      392      +26     
  Partials        2        2

Impacted Files	Coverage Δ
src/commands/eject.ts	100% <100%> (ø)	:white_check_mark:
src/registerCommands.ts	100% <ø> (ø)	:white_check_mark:
src/command.ts	100% <ø> (ø)	:white_check_mark:

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