I'm trying to install grav on a device running lighttpd that only supports php 7.1.1 so trying this version https://github.com/getgrav/grav/releases/tag/1.5.7 however i'm getting the following error
**Fatal error** : Uncaught Error: Call to undefined function Grav\Common\Config\json_encode() in /grav/grav/system/src/Grav/Common/Config/CompiledBlueprints.php:36 Stack trace: #0 /grav/grav/system/src/Grav/Common/Config/CompiledBase.php(248): Grav\Common\Config\CompiledBlueprints->checksum() #1 /grav/grav/system/src/Grav/Common/Config/CompiledBase.php(116): Grav\Common\Config\CompiledBase->saveCompiledFile('/grav/grav/cach...') #2 /grav/grav/system/src/Grav/Common/Service/ConfigServiceProvider.php(73): Grav\Common\Config\CompiledBase->load() #3 /grav/grav/system/src/Grav/Common/Service/ConfigServiceProvider.php(31): Grav\Common\Service\ConfigServiceProvider::blueprints(Object(Grav\Common\Grav)) #4 /grav/grav/vendor/pimple/pimple/src/Pimple/Container.php(118): Grav\Common\Service\ConfigServiceProvider->Grav\Common\Service\{closure}(Object(Grav\Common\Grav)) #5 /grav/grav/system/src/Grav/Common/Service/ConfigServiceProvider.php(98): Pimple\Container->offsetGet('blueprints') #6 /grav/grav/system/src/Grav/Common/Data/Data.php(229 in **/grav/grav/system/src/Grav/Common/Config/CompiledBlueprints.php** on line **36**