Update mongodb driver version to 3.x

[mpangrazzi]

Hi,

I've updated the mongo dep to ^3.2.3, following the changes reported here.

What I did so far:

• upgraded mongo dep to ^3.2.3 (should fix Upgrade to Mongo 3.0.10 #257 and mongodb version #260 )
• deprecated the support of collection.geoNear (as mongo 3.2.3 did)
• used by default the new url parser (should fix Add support for Mongo 3.6 connection strings #251)
• updated docs for collection.findOneAndUpdate and geoNear
• added deprecation log for collection.group command

I didn't implement or support any new features ATM (such as retryable writes or change streams).

All tests are passing, although there are some deprecation logs.
Since there are some breaking API changes, this could be a major version update.

[codecov-io]

Codecov Report

Merging #273 into master will increase coverage by 0.24%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #273      +/-   ##
==========================================
+ Coverage   94.57%   94.81%   +0.24%     
==========================================
  Files           6        6              
  Lines         387      386       -1     
==========================================
  Hits          366      366              
+ Misses         21       20       -1

Impacted Files	Coverage Δ
lib/manager.js	95.48% <100%> (+0.87%)	⬆️
lib/collection.js	94.28% <100%> (-0.11%)	⬇️

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[gflores]

Please merge it soon, I really need the v3

[mathieudutour]

Thanks for the PR!

[mathieudutour]

just a few comments in the docs and then I'll merge this

[mathieudutour]

🙏