Retry launching browser if first time fails

This is a first attempt at fixing #128. It's unlikely to fix the issue completely, or even at all, as the browser will sometimes crash after testing several URLs and we don't have any logic to reopen a browser that has crashed mid-tests.

lib/pa11y-ci.js

@@ -41,7 +41,20 @@ module.exports.defaults = {
 function pa11yCi(urls, options) {
 	return new Promise(async resolve => {
 		// Create a test browser to assign to tests
-		const testBrowser = await puppeteer.launch(options.chromeLaunchConfig);
+		let testBrowser;
+
+		// Issue #128: on specific URLs, puppeteer will sometimes fail to load
+		//  with a bunch of different, unhelpful errors. This will reattempt to
+		//  relaunch the browser once before bailing out
+		try {
+			testBrowser = await puppeteer.launch(
+				options.chromeLaunchConfig
+			);
+		} catch (error) {
+			testBrowser = await puppeteer.launch(
+				options.chromeLaunchConfig
+			);
+		}
 
 		// Default the passed in options
 		options = defaults({}, options, module.exports.defaults);
@@ -52,7 +65,6 @@ function pa11yCi(urls, options) {
 		const log = options.log;
 		delete options.log;
 
-
 		// Create a Pa11y test function and an async queue
 		const taskQueue = queue(testRunner, options.concurrency);
 		taskQueue.drain = testRunComplete;