revert: commit a0d1856 that changed the bootloader.

The `config()` method of `Application` doesn't exist in the current Acorn (v4.3.1) and this new bootloader code is not apart of Sage v10.8.2, but for an upcoming version of Sage.

Fixes PHP error: "Fatal error: Uncaught BadMethodCallException: Method Roots\Acorn\Application::configure does not exist." by reverting the code changed in commit a0d1856.

Author: yCodeTech

functions.php

@@ -1,7 +1,5 @@
 <?php
 
-use Roots\Acorn\Application;
-
 /*
 |--------------------------------------------------------------------------
 | Register The Auto Loader
@@ -31,11 +29,18 @@
 |
 */
 
-Application::configure()
-	->withProviders([
-		App\Providers\ThemeServiceProvider::class,
-	])
-	->boot();
+if (! function_exists('\Roots\bootloader')) {
+	wp_die(
+		__('You need to install Acorn to use this theme.', 'sage'),
+		'',
+		[
+			'link_url' => 'https://roots.io/acorn/docs/installation/',
+			'link_text' => __('Acorn Docs: Installation', 'sage'),
+		]
+	);
+}
+
+\Roots\bootloader()->boot();
 
 /*
 |--------------------------------------------------------------------------