Pulling in Thor changes to print friendly error on ambiguous command

[ssrihari]

Fixes #2550

[gnufied]

Thank you for opening this PR. It needs wee bit more work though:

nomads/bundler git:(master)* ruby -S ./bin/bundle i
nomads/bundler git:(master)* 

Which means it silently returns the prompt rather than printing the actual error. The reason it prints nothing is because - Bundler.ui does not really point to a printable logger yet. Only when Bundler::CLI is initialized it points to something that can actually print.

[indirect]

@gnufied the RailsGirls team has a patch (with tests) that fixes those things, so I'll update Thor on master and let them know they can catch the new exception.

@ssrihari thanks for getting this fixed in Thor!

[indirect]

Changes merged as part of 04f8e4b.