Elgg 1.12.11 with PHP 7

Whenever I am trying to run elgg 1.12.11 on PHP 7, it is showing the following error:

Fatal error: 
Uncaught Error: Call to undefined function Elgg\mysql_real_escape_string() in /home/ckarma/public_html/engine/classes/Elgg/Database.php:651 
Stack trace: 
#0 /home/ckarma/public_html/engine/lib/database.php(141): Elgg\Database->sanitizeString('cookies') 
#1 /home/ckarma/public_html/engine/classes/Elgg/Database/ConfigTable.php(165): sanitize_string('cookies') 
#2 /home/ckarma/public_html/engine/classes/Elgg/Config.php(111): Elgg\Database\ConfigTable->get('cookies', 0) 
#3 /home/ckarma/public_html/engine/classes/Elgg/Di/ServiceProvider.php(207): Elgg\Config->get('cookies') 
#4 [internal function]: Elgg\Di\ServiceProvider->Elgg\Di\{closure}(Object(Elgg\Di\ServiceProvider)) 
#5 /home/ckarma/public_html/engine/classes/Elgg/Di/DiContainer.php(76): call_user_func(Object(Closure), Object(Elgg\Di\ServiceProvider)) 
#6 /home/ckarma/public_html/engine/classes/Elgg/Di/DiContainer.php(56): Elgg\Di\DiContainer->build(Object(Closure), 'session') 
#7 /home/ckarma/public_html/engine/lib/sessions.php(61): Elgg\Di\DiContainer->__get('se in /home/ckarma/public_html/engine/classes/Elgg/Database.php on line 651

Kindly help!