fix(@angular/cli): show warnings on serve

The new function already correctly prints warnings/errors.

Followup to #6989
Fix #7213

Author: filipesilva

packages/@angular/cli/tasks/serve.ts

@@ -215,14 +215,8 @@ export default Task.extend({
     const server = new WebpackDevServer(webpackCompiler, webpackDevServerConfiguration);
     if (!serveTaskOptions.verbose) {
       webpackCompiler.plugin('done', (stats: any) => {
-        const str = statsToString(stats.toJson(), statsConfig);
-        if (stats.hasErrors()) {
-          this.ui.writeError(str);
-        } else if (stats.hasWarnings()) {
-          this.ui.writeWarnLine(str);
-        } else {
-          this.ui.writeLine(str);
-        }
+        const str = statsToString(stats.toJson('verbose'), statsConfig);
+        this.ui.writeLine(str);
       });
     }