Fix e2e tests

[thislooksfun]

The vue-cli-plugin-electron-builder v2.0.0 beta has a fix for the issue outlined in tests/e2e/electron.spec.js

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Steps to fix:

1. Switch to vue-cli-plugin-electron-builder v2.0.0 beta
2. Pass correct spectron version to testWithSpectron()

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References:

• Calling testWithSpectron() opens infinite windows nklayman/vue-cli-plugin-electron-builder#467
• Calling testWithSpectron() opens infinite windows nklayman/vue-cli-plugin-electron-builder#467 (comment)

• earthdawn/tests/e2e/electron.spec.js

  Lines 13 to 21 in c0e82ba

  	// TODO: THIS CALL IS BUGGED
  	// BODY: Calling this function causes it to open as many windows as it can
  	// BODY: until it times out
  	// BODY: (pending nklayman/vue-cli-plugin-electron-builder#467)
  	return testWithSpectron().then(instance => {
  	app = instance.app;
  	stopServe = instance.stopServe;
  	});

[thislooksfun]

This is now pending nklayman/vue-cli-plugin-electron-builder#647