composer require mongodb/mongodb --ignore-platform-reqs
composer require jenssegers/mongodb --ignore-platform-reqs

Using version ^3.4 for jenssegers/mongodb
./composer.json has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)
Package operations: 2 installs, 0 updates, 0 removals
  - Installing mongodb/mongodb (1.4.2): Downloading (100%)         
  - Installing jenssegers/mongodb (v3.4.5): Downloading (100%)         
jenssegers/mongodb suggests installing jenssegers/mongodb-session (Add MongoDB session support to Laravel-MongoDB)
jenssegers/mongodb suggests installing jenssegers/mongodb-sentry (Add Sentry support to Laravel-MongoDB)
Writing lock file
Generating optimized autoload files