Replace remaining $a->isInstallMode() instances

src/Core/Console/Maintenance.php

@@ -64,7 +64,7 @@ HELP;
 			throw new \Asika\SimpleConsole\CommandArgsException('Too many arguments');
 		}
 
-		if ($a->isInstallMode()) {
+		if (App\Mode::isInstall()) {
 			throw new \RuntimeException('Database isn\'t ready or populated yet');
 		}