Do not include sourcemap files in Service Worker shell

Fixes #534

test/apps/with-sourcemaps-webpack/test.ts

@@ -0,0 +1,43 @@
+import * as puppeteer from 'puppeteer';
+import { build } from '../../../api';
+import * as assert from "assert";
+import { AppRunner } from '../AppRunner';
+import * as fs from "fs";
+import * as path from "path";
+
+describe('with-sourcemaps-webpack', function() {
+	this.timeout(10000);
+
+	let runner: AppRunner;
+	let page: puppeteer.Page;
+	let base: string;
+
+	// helpers
+	let start: () => Promise<void>;
+	let prefetchRoutes: () => Promise<void>;
+	let prefetch: (href: string) => Promise<void>;
+	let goto: (href: string) => Promise<void>;
+
+	// hooks
+	before(async () => {
+		await build({ cwd: __dirname, bundler: 'webpack' });
+
+		runner = new AppRunner(__dirname, '__sapper__/build/server/server.js');
+		({ base, page, start, prefetchRoutes, prefetch, goto } = await runner.start());
+	});
+
+	it('does not put sourcemap files in service worker shell', async () => {
+		const serviceWorker = await import(`${__dirname}/__sapper__/service-worker.js`);
+		const shell: string[] = serviceWorker.shell;
+
+		assert.equal(shell.filter(_ => _.endsWith('.map')).length, 0,
+			'sourcemap files are not cached in SW');
+
+		const clientShellDir = path.resolve(`${__dirname}/__sapper__/build`, path.dirname(shell[0]));
+		const sourcemapFiles = fs.readdirSync(clientShellDir).filter(_ => _.endsWith('.map'));
+		assert.ok(sourcemapFiles.length > 0, 'sourcemap files exist');
+	});
+
+	after(() => runner.end());
+
+});