feat: Add support for pnpm

[Alxandr]

Naively implemented, and currently untested. I've updated my project that uses pnpm (YoloDev/rollup-config) to install my fork instead of the package published to npm, so now I just have to wait for a new update to a dependency to see if it really works or not.

[ExE-Boss]

I am getting the following with this:

> @exe-boss/x.smwc-style@0.1.0 lint /home/travis/build/ExE-Boss/smwc-style
> gulp lint && eslint **/*.js

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

Error: Cannot find module 'homedir-polyfill'
    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:22:18)
    at Object.<anonymous> (/home/travis/build/ExE-Boss/smwc-style/node_modules/.registry.npmjs.org/expand-tilde/2.0.2/node_modules/expand-tilde/index.js:8:15)
    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)

https://travis-ci.com/ExE-Boss/smwc-style/builds/102027920#L584