feat: Support Cypress 5 (component-driven#72)

- [x] Allow Cypress 5 in peer dependencies
- [x] Use `cy.readFile` to load Axe source because `axe.source` is causing a `exports is not defined` error in Cypress 5
- [x] Add integration test

Fixes component-driven#56

cypress.json

@@ -0,0 +1,4 @@
+{
+  "baseUrl": "http://localhost:8080",
+  "video": false
+}

cypress/fixtures/example.json

@@ -0,0 +1,5 @@
+{
+  "name": "Using fixtures to represent data",
+  "email": "[email protected]",
+  "body": "Fixtures are a great way to mock data for responses to routes"
+}

cypress/integration/test.js

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+it('works!', () => {
+	cy.visit('/');
+	cy.injectAxe();
+	cy.checkA11y();
+});

cypress/plugins/index.js

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+/// <reference types="cypress" />
+// ***********************************************************
+// This example plugins/index.js can be used to load plugins
+//
+// You can change the location of this file or turn off loading
+// the plugins file with the 'pluginsFile' configuration option.
+//
+// You can read more here:
+// https://on.cypress.io/plugins-guide
+// ***********************************************************
+
+// This function is called when a project is opened or re-opened (e.g. due to
+// the project's config changing)
+
+/**
+ * @type {Cypress.PluginConfig}
+ */
+// eslint-disable-next-line no-unused-vars
+module.exports = (on, config) => {
+	// `on` is used to hook into various events Cypress emits
+	// `config` is the resolved Cypress config
+};

cypress/support/commands.js

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+// ***********************************************
+// This example commands.js shows you how to
+// create various custom commands and overwrite
+// existing commands.
+//
+// For more comprehensive examples of custom
+// commands please read more here:
+// https://on.cypress.io/custom-commands
+// ***********************************************
+//
+//
+// -- This is a parent command --
+// Cypress.Commands.add("login", (email, password) => { ... })
+//
+//
+// -- This is a child command --
+// Cypress.Commands.add("drag", { prevSubject: 'element'}, (subject, options) => { ... })
+//
+//
+// -- This is a dual command --
+// Cypress.Commands.add("dismiss", { prevSubject: 'optional'}, (subject, options) => { ... })
+//
+//
+// -- This will overwrite an existing command --
+// Cypress.Commands.overwrite("visit", (originalFn, url, options) => { ... })

cypress/support/index.js

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+// ***********************************************************
+// This example support/index.js is processed and
+// loaded automatically before your test files.
+//
+// This is a great place to put global configuration and
+// behavior that modifies Cypress.
+//
+// You can change the location of this file or turn off
+// automatically serving support files with the
+// 'supportFile' configuration option.
+//
+// You can read more here:
+// https://on.cypress.io/configuration
+// ***********************************************************
+
+// Import commands.js using ES2015 syntax:
+import './commands';
+
+// Import compiled cypress-axe
+import '../../dist';