databases/pecl-mongodb: update 1.9.1 -> 1.12.0

Relnotes:
https://github.com/mongodb/mongo-php-driver/releases/tag/1.12.0
https://github.com/mongodb/mongo-php-driver/releases/tag/1.11.1
https://github.com/mongodb/mongo-php-driver/releases/tag/1.11.0
https://github.com/mongodb/mongo-php-driver/releases/tag/1.10.0
https://github.com/mongodb/mongo-php-driver/releases/tag/1.9.2