test fail to run on recent nodejs

[christophe-g]

I'll provide a fix in the coming days - along with an upgrade to ES6 modules (for reductio, universe and crossfliter), if everything runs smoothly.

npm run test

> reductio@0.6.3 test /home/christophe/Programming/Polymer/litElement/reductio
> ./node_modules/karma/bin/karma start --browsers PhantomJS --single-run

/home/christophe/Programming/Polymer/litElement/reductio/node_modules/socket.io/lib/store.js:35
Store.prototype.__proto__ = EventEmitter.prototype;
                                         ^

TypeError: Cannot read property 'prototype' of undefined
    at Object.<anonymous> (/home/christophe/Programming/Polymer/litElement/reductio/node_modules/socket.io/lib/store.js:35:42)
    at Module._compile (internal/modules/cjs/loader.js:778:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:789:10)
    at Module.load (internal/modules/cjs/loader.js:653:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:593:12)
    at Function.Module._load (internal/modules/cjs/loader.js:585:3)
    at Module.require (internal/modules/cjs/loader.js:692:17)
    at require (internal/modules/cjs/helpers.js:25:18)
    at Object.<anonymous> (/home/christophe/Programming/Polymer/litElement/reductio/node_modules/socket.io/lib/manager.js:16:13)
    at Module._compile (internal/modules/cjs/loader.js:778:30)
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! reductio@0.6.3 test: `./node_modules/karma/bin/karma start --browsers PhantomJS --single-run`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the reductio@0.6.3 test script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /home/christophe/.npm/_logs/2019-10-03T14_03_31_075Z-debug.log