Fix generating import statement code

[antxln]

Reference: #892

Code generator is appending a dot at end of module name in import statement, which is throwing an error with black. Maybe the dot can be prepended since it is indicating path heirarchy levels?

[codecov]

Codecov Report

Base: 100.00% // Head: 100.00% // No change to project coverage 👍

Coverage data is based on head (9753f7b) compared to base (e9b6edf).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff             @@
##            master      #893     +/-   ##
===========================================
  Coverage   100.00%   100.00%             
===========================================
  Files           11        14      +3     
  Lines         1020      2047   +1027     
  Branches       201       474    +273     
===========================================
+ Hits          1020      2047   +1027     

Flag	Coverage Δ
unittests	100.00% <100.00%> (?)

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

Impacted Files	Coverage Δ
datamodel_code_generator/__main__.py	100.00% <100.00%> (ø)
datamodel_code_generator/http.py	100.00% <100.00%> (ø)
datamodel_code_generator/model/base.py	100.00% <100.00%> (ø)
datamodel_code_generator/model/enum.py	100.00% <100.00%> (ø)
...amodel_code_generator/model/pydantic/base_model.py	100.00% <100.00%> (ø)
..._code_generator/model/pydantic/custom_root_type.py	100.00% <100.00%> (ø)
...tamodel_code_generator/model/pydantic/dataclass.py	100.00% <100.00%> (ø)
datamodel_code_generator/model/pydantic/imports.py	100.00% <100.00%> (ø)
datamodel_code_generator/model/pydantic/types.py	100.00% <100.00%> (ø)
datamodel_code_generator/parser/base.py	100.00% <100.00%> (ø)
... and 7 more

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[koxudaxi]

@antxln
Thank you for creating the PR.
I have released a new version as 0.13.5