[5.3] Fix line breaks in plain text email (#15115)

* Fix line breaks in plain text email

* Keep it uniform

src/Illuminate/Notifications/resources/views/email-plain.blade.php

@@ -1,22 +1,22 @@
 <?php
-if ($greeting !== null) {
-    echo e($greeting);
+
+if (! empty($greeting)) {
+    echo $greeting, "\n\n";
 } else {
-    echo $level == 'error' ? 'Whoops!' : 'Hello!';
+    echo $level == 'error' ? 'Whoops!' : 'Hello!', "\n\n";
 }
 
 if (! empty($introLines)) {
-    echo implode("\r\n", $introLines), "\r\n\r\n";
+    echo implode("\n", $introLines), "\n\n";
 }
 
 if (isset($actionText)) {
-    echo "{$actionText}: {$actionUrl}\r\n\r\n";
+    echo "{$actionText}: {$actionUrl}", "\n\n";
 }
 
 if (! empty($outroLines)) {
-    echo implode("\r\n", $outroLines), "\r\n\r\n";
+    echo implode("\n", $outroLines), "\n\n";
 }
-?>
 
-Regards,
-{{ config('app.name') }}
+echo 'Regards,', "\n";
+echo config('app.name'), "\n";