fix: switch Stackblitz back to npm

Lately the dependency installs when forking to Stackblitz have been really slow. It seems like switching back to npm speeds them up significantly (from ~5min to ~30s).

Also updates the Angular version which has a much smaller bundle size. Note that just doing this didn't help much for yarn which was getting stuck for a long time after the packages are installed.

Author: crisbeto

material.angular.io/src/app/shared/stack-blitz/stack-blitz-writer.ts

@@ -36,7 +36,7 @@ export const TEMPLATE_FILES = [
   'angular.json',
   'karma.conf.js',
   'package.json',
-  'yarn.lock',
+  'package-lock.json',
   'tsconfig.app.json',
   'tsconfig.json',
   'tsconfig.spec.json',
@@ -202,7 +202,8 @@ export class StackBlitzWriter {
         .replace(/material-docs-example/g, data.selectorName)
         .replace(/\${title}/g, data.description);
     } else if (fileName === '.stackblitzrc') {
-      fileContent = fileContent.replace(/\${startCommand}/, isTest ? 'yarn test' : 'yarn start');
+      fileContent = fileContent.replace(/\${startCommand}/,
+        isTest ? 'npm run test' : 'npm run start');
     } else if (fileName === 'src/main.ts') {
       const mainComponentName = data.componentNames[0];