Issue with Laravel Forge (Repository Installation)

I'm trying to deploy my very first laravel project in forge but I got this error upon Git repository installation:

Generating autoload files

php artisan clear-compiled PHP Parse error: syntax error, unexpected '<<' (T_SL), expecting ']' in /home/forge/default/config/app.php on line 139

PHP Stack trace:

PHP 1. {main}() /home/forge/default/artisan:0

PHP 2. Illuminate\Foundation\Console\Kernel->handle() /home/forge/default/artisan:36 PHP 3. Illuminate\Foundation\Console\Kernel->bootstrap() /home/forge/default/vendor/laravel/framework/src/Illuminate/Foundation/Console/Kernel.php:98 PHP 4. Illuminate\Foundation\Application->bootstrapWith() /home/forge/default/vendor/laravel/framework/src/Illuminate/Foundation/Console/Kernel.php:201 PHP 5. Illuminate\Foundation\Bootstrap\LoadConfiguration->bootstrap() /home/forge/default/vendor/laravel/framework/src/Illuminate/Foundation/Application.php:203 PHP 6. Illuminate\Foundation\Bootstrap\LoadConfiguration->loadConfigurationFiles() /home/forge/default/vendor/laravel/framework/src/Illuminate/Foundation/Bootstrap/LoadConfiguration.php:38

Parse error: syntax error, unexpected '<<' (T_SL), expecting ']' in /home/forge/default/config/app.php on line 139

Call Stack: 0.0002 221680 1. {main}() /home/forge/default/artisan:0 0.0205 1946936 2. Illuminate\Foundation\Console\Kernel->handle() /home/forge/default/artisan:36 0.0205 1947080 3. Illuminate\Foundation\Console\Kernel->bootstrap() /home/forge/default/vendor/laravel/framework/src/Illuminate/Foundation/Console/Kernel.php:98 0.0205 1947248 4. Illuminate\Foundation\Application->bootstrapWith() /home/forge/default/vendor/laravel/framework/src/Illuminate/Foundation/Console/Kernel.php:201 0.0231 2110856 5. Illuminate\Foundation\Bootstrap\LoadConfiguration->bootstrap() /home/forge/default/vendor/laravel/framework/src/Illuminate/Foundation/Application.php:203 0.0235 2139760 6. Illuminate\Foundation\Bootstrap\LoadConfiguration->loadConfigurationFiles() /home/forge/default/vendor/laravel/framework/src/Illuminate/Foundation/Bootstrap/LoadConfiguration.php:38

Script php artisan clear-compiled handling the post-install-cmd event returned with an error

[RuntimeException]
Error Output: PHP Parse error: syntax error, unexpected '<<' (T_SL), expecting ']' in /home/forge/default/config/app.php on line 139
PHP Stack trace:
PHP 1. {main}() /home/forge/default/artisan:0
PHP 2. Illuminate\Foundation\Console\Kernel->handle() /home/forge/default/artisan:36
PHP 3. Illuminate\Foundation\Console\Kernel->bootstrap() /home/forge/default/vendor/laravel/framework/src/Illuminate/Foundation/Console/Kernel.php:98
PHP 4. Illuminate\Foundation\Application->bootstrapWith() /home/forge/default/vendor/laravel/framework/src/Illuminate/Foundation/Console/Kernel.php:201
PHP 5. Illuminate\Foundation\Bootstrap\LoadConfiguration->bootstrap() /home/forge/default/vendor/laravel/framework/src/Illuminate/Foundation/Application.php:203
PHP 6. Illuminate\Foundation\Bootstrap\LoadConfiguration->loadConfigurationFiles() /home/forge/default/vendor/laravel/framework/src/Illuminate/Foundation/Bootstrap/LoadConfiguration.php:38

via Chebli Mohamed