attach request to custom exception

[beliaev-maksim]

closes #588

[codecov]

Codecov Report

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

Coverage data is based on head (032873c) compared to base (b30c13f).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #614   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            9         9           
  Lines         2789      2801   +12     
=========================================
+ Hits          2789      2801   +12     

Impacted Files	Coverage Δ
responses/__init__.py	100.00% <100.00%> (ø)
responses/tests/test_responses.py	100.00% <100.00%> (ø)

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report at Codecov.
📢 Do you have feedback about the report comment? Let us know in this issue.