fix serialize embedded relationships

fix dsn config when not unix socket

 Fix #1293: Exception: BelongsToMany Is Not supported for hybrid query constraints! #1324 

Without this statement, the reaffirming of belongsToMany relations would fail. The original commit was to prove a point in an issue, but for it to work in the real world this extra bit is added.

This temporarily skirts around the issue described in the following issue: https://github.com/jenssegers/laravel-mongodb/issues/1293

Fix drop index

Updated DatabaseFailedJobProvider

Fixes bug that prevents dropping compound indexes with multiple fields.
Indexes can now be dropped by name or column list, adhering to the Illuminate Blueprint interface.

Updated DatabaseFailedJobProvider to return object(s) instead of arrays as defined by the FailedJobProviderInterface.
Fixes a bug that caused queue:retry to fail when using mongodb for failed jobs.

[Fix] Unable to delete nested embedded models

Merge latest from jenssegers/laravel-mongodb:master

Update README.md

Version Support update

Laravel 5.6 support