Fix desktop database path retrieval

[vitusortner]

We're now referring to the abstract DatabaseFactory.getDatabasesPath instead of the mobile implementation (can be found at sqflite.getDatabasesPath).

Closes #474

[codecov]

Codecov Report

Merging #475 (b72be61) into develop (5d9c888) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff            @@
##           develop     #475   +/-   ##
========================================
  Coverage    83.40%   83.40%           
========================================
  Files           68       68           
  Lines         1687     1687           
========================================
  Hits          1407     1407           
  Misses         280      280           

Flag	Coverage Δ
floor	83.40% <0.00%> (ø)
floor_generator	83.29% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
floor/lib/src/sqflite_database_factory.dart	54.54% <0.00%> (ø)

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