Doesn't work with Yarn PnP

The injectAxe command currently directly looks for the node_modules folder to get axe-core source code. This - however - makes it incompatible with Yarn Plug'n'Play, since it doesn't rely on node_modules.

I worked it around by overwriting the injectAxe command in this way:

Cypress.Commands.overwrite('injectAxe', () => {
  cy.task('getAxeSource').then(axeSource =>
    cy.window({ log: false }).then(window => {
      const script = window.document.createElement('script');
      script.innerHTML = axeSource;
      window.document.head.appendChild(script);
    }),
  );
});

And adding this task to my Cypress plugins:

const axe = require('axe-core/axe.js');

module.exports = (on, config) => {
  on('task', {
    getAxeSource: () => axe.source,
  });
};

In this way, the task (that runs in Node) handles the require logic, while the command (that runs in the browser) gets the source from the task and injects it. This would probably also solve https://github.com/component-driven/cypress-axe/issues/73, which is somewhat related.

Let me know if you think this solution makes sense to you. If so, I will open a PR.

Start by locating the injectAxe command and the Cypress plugins configuration that currently obtains axe-core source from node_modules. Compare that flow with the proposed getAxeSource task and verify that axe-core can be loaded under Yarn Plug'n'Play and injected in the browser without node_modules; done means injectAxe works in a Yarn PnP project.