Uninstall command

[decioferreira]

Fixes #47.

[decioferreira]

Currently failing to remove elm/browser for the guida-lang/compiler project. It seems to relate to the test indirect dependencies:

% ./bin/index.js install elm/browser 
Here is my plan:
  
  Add:
                  elm/browser 1.0.2

Would you like me to update your elm.json accordingly? [Y/n]: 
Success!
% ./bin/index.js uninstall elm/browser
Here is my plan:
  
  Remove:
                  elm/browser 1.0.2

Would you like me to update your elm.json accordingly? [Y/n]: 
-- ERROR IN DEPENDENCIES ---------------------------------------------- elm.json

It looks like the dependencies elm.json in were edited by hand (or by a 3rd
party tool) leaving them in an invalid state.

Try to change them back to what they were before! It is much more reliable to
add dependencies with elm install.

Please ask for help on the community forums if you try those paths and are still
having problems!