Fix one-to-many field lookup to use model name

[stphivos]

This only holds when foreign key related name is not set.

[codecov-io]

Codecov Report

Merging #41 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #41   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           6      6           
  Lines         634    634           
=====================================
  Hits          634    634

Impacted Files	Coverage Δ
django_mock_queries/query.py	100% <100%> (ø)	✅
django_mock_queries/utils.py	100% <100%> (ø)	✅

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