rm-cli is broken on case-sensitive FSes

[sqs]

Reported at https://gitlab.com/jez9999/rm-cli/issues/1, MR with fix at https://gitlab.com/jez9999/rm-cli/merge_requests/1 was ignored.

This results in an error when running rm-cli (eg via an npm run script`), like:

hq:~/src/github.com/sourcegraph/react-loading-spinner $ npm run build

> @sourcegraph/react-loading-spinner@0.0.0-development clean /home/sqs/src/github.com/sourcegraph/react-loading-spinner
> rm-cli -r lib/

internal/modules/cjs/loader.js:583
    throw err;
    ^

Error: Cannot find module 'Bluebird'
    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:581:15)
    at Function.Module._load (internal/modules/cjs/loader.js:507:25)
    at Module.require (internal/modules/cjs/loader.js:637:17)
    at require (internal/modules/cjs/helpers.js:20:18)
    at Object.<anonymous> (/home/sqs/src/github.com/sourcegraph/react-loading-spinner/node_modules/rm-cli/src/rm-cli.js:9:17)
    at Module._compile (internal/modules/cjs/loader.js:689:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:700:10)
    at Module.load (internal/modules/cjs/loader.js:599:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:538:12)
    at Function.Module._load (internal/modules/cjs/loader.js:530:3)
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! @sourcegraph/react-loading-spinner@0.0.0-development clean: `rm-cli -r lib/`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the @sourcegraph/react-loading-spinner@0.0.0-development clean script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

You can use npm uninstall rm-cli && npm install --save-dev del-cli and then del-cli 'lib/**/*' instead.