Importing uplink from master fails without pydantic

[DonutByte]

Describe the bug
If I import uplink from master branch without first installing the pydantic package, Python throws an error:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "c:\temp\venv\lib\site-packages\uplink\__init__.py", line 2, in <module>
    from uplink import returns, types
  File "c:\temp\venv\lib\site-packages\uplink\returns.py", line 6, in <module>
    from uplink import decorators
  File "c:\temp\venv\lib\site-packages\uplink\decorators.py", line 11, in <module>
    from uplink import arguments, helpers, hooks, interfaces, utils
  File "c:\temp\venv\lib\site-packages\uplink\arguments.py", line 14, in <module>
    from uplink.converters import keys
  File "c:\temp\venv\lib\site-packages\uplink\converters\__init__.py", line 18, in <module>
    from uplink.converters.pydantic_ import PydanticConverter
  File "c:\temp\venv\lib\site-packages\uplink\converters\pydantic_.py", line 1, in <module>
    import pydantic
ModuleNotFoundError: No module named 'pydantic'

To Reproduce
Steps to reproduce the behavior:

1. install uplink from master (pip install git+https://github.com/prkumar/uplink.git@master)
2. python -c "import uplink"

Expected behavior
uplink shouldn't require pydantic to be installed

Additional context
Looks like removing this line, fixes the issue:

uplink/uplink/converters/pydantic_.py

Line 1 in 87bdc5d

import pydantic

I will link a PR that does this change 😄