See: https://github.com/mongodb/docs/commit/2a912319800d932b5fd5dc2dfee3d591e4311b9f

This bumps the extension requirement to 1.2.0. Composer allows dev versions with the "^" operator, so this will accept 1.2.0alpha3, which introduces a "collation" option for Query and BulkWrite methods.

GridFS streams do not yet support seeking (PHPLIB-213), and HHVM requires a stream_seek() implementation in order to pass a non-negative offset to stream_get_contents().