Nextcloud 21 runs on PHP 7.3+ only

Signed-off-by: Morris Jobke <hey@morrisjobke.de>

lib/versioncheck.php

@@ -22,10 +22,10 @@
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  *
  */
-// Show warning if a PHP version below 7.2 is used,
-if (PHP_VERSION_ID < 70200) {
+// Show warning if a PHP version below 7.3 is used,
+if (PHP_VERSION_ID < 70300) {
 	http_response_code(500);
-	echo 'This version of Nextcloud requires at least PHP 7.2<br/>';
+	echo 'This version of Nextcloud requires at least PHP 7.3<br/>';
 	echo 'You are currently running ' . PHP_VERSION . '. Please update your PHP version.';
 	exit(-1);
 }