Fix heredoc syntax (#3426)

Fix regression from https://github.com/FreshRSS/FreshRSS/pull/3407

Identifier must not be indented

PHP 5.6.36 (cli) (built: Apr 28 2018 21:14:51)
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PHP Parse error:  syntax error, unexpected end of file in
lib/lib_rss.php on line 608
Errors parsing lib/lib_rss.php

lib/lib_rss.php

@@ -603,5 +603,5 @@ function errorMessage($errorTitle, $error = '') {
 	<p>More logs can be generated by enabling <code>'environment' => 'development',</code> in <code>./FreshRSS/data/config.php</code></p>
 	<p>Running the feed update script (with the same user and PHP version as your Web server) might provide other hints, e.g.:
 		<code>sudo -u www-data /usr/bin/php ./FreshRSS/app/actualize_script.php</code></p>
-	MSG;
+MSG;
 }