callEffect assumes non generator with array syntax fn

First off: thanks for the lib!

I'm attempting to use cofx inside class generator functions. I want to maintain the context of this when using these functions. To maintain context, I use the array style of passing fn: call([obj, 'methodName']). However, it seems that the callEffect handler assumes a non-generator function when you pass the array syntax, and immediately tries to resolve it, instead of testing for a generator and running it. Ex:

const { call, task } = require('cofx');

class TheClass {
    constructor() {

    }

    asyncThing() {
        return new Promise((resolve) => {
            setTimeout(() => resolve(3), 1000);
        })
    }

    * levelThree() {
        const a = yield call(this.asyncThing);
        const b = yield call(this.asyncThing);
        return a + b;
    }

    * levelTwo() {
        const a = yield call([this, 'levelThree']);
        const b = yield call([this, 'levelThree']);
        return a + b;
    }

    * levelOne() {
        const results = yield call([this, 'levelTwo']);
        return results;
    }
}

const c = new TheClass;

task.call(c, c.levelOne)
    .then(results => console.log(results));

If I run this the resulting log is an empty object that outputs immediately. If I change this bit in callEffect to:

let gen;
if (Array.isArray(fn)) {
    const [obj, fnName, ...fargs] = fn;
    gen = obj[fnName](...fargs);
} else {
    gen = fn.call(this, ...args);
}

Then the above code gets all of its generators run, waits for the timeouts, and outputs: 12.

I'm happy to submit a PR if my assumptions here are correct.

neurosnap / cofx

callEffect assumes non generator with array syntax fn #12