It is an error to omit the modes in options

[akabekobeko]

Example:

const icongen = require( 'icon-gen' );

icongen( './test/data/sample.svg', './test', { report: true } )
.then( ( results ) => {
  console.log( results );
} )
.catch( ( err ) => {
  console.error( err );
} );

Error:

TypeError: Cannot read property 'forEach' of undefined
    at Function.generate (.../icon-gen/lib/icon-generator.js:161:12)
    at .../icon-gen/lib/icon-generator.js:84:25
    at .../icon-gen/lib/png-generator.js:92:11

Because the modes is undefined in IconGenerator.generate.