fix: nested relations not getting normalized correctly

[kiaking]

This PR fixes the nested relationship normalization error.

Type of PR:

• Bugfix
• Feature
• Refactor
• Code style update
• Build-related changes
• Test
• Documentation
• Other, please describe:

Breaking changes:

• No
• Yes

[codecov]

Codecov Report

Merging #50 (20fe89d) into master (f82488a) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #50   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           36        36           
  Lines          822       823    +1     
  Branches       131       132    +1     
=========================================
+ Hits           822       823    +1     

Impacted Files	Coverage Δ
src/model/Model.ts	100.00% <100.00%> (ø)
src/model/attributes/relations/BelongsTo.ts	100.00% <100.00%> (ø)
src/model/attributes/relations/HasMany.ts	100.00% <100.00%> (ø)
src/model/attributes/relations/HasManyBy.ts	100.00% <100.00%> (ø)
src/model/attributes/relations/HasOne.ts	100.00% <100.00%> (ø)
src/schema/Schema.ts	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f82488a...20fe89d. Read the comment docs.