Fix usage of response_types_map inside API client's call_api method.

[ndhansen]

Fixes #310

I didn't add tests because I couldn't see any existing tests for the call_api method, but if I missed it, please let me know.

(This is a copy of MR #311, but I needed to resolve a conflict and accidentally had been working on the master branch.)

[tomplus]

LGTM

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 27.06%. Comparing base (abd4624) to head (e3bf336).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #362   +/-   ##
=======================================
  Coverage   27.06%   27.06%           
=======================================
  Files         805      805           
  Lines       98720    98722    +2     
=======================================
+ Hits        26717    26719    +2     
  Misses      72003    72003           

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[tomplus]

Thank you!