change logic of _get_url_and_path to comply with RFC 3986

[beliaev-maksim]

closes #506

[codecov]

Codecov Report

Merging #507 (179bda0) into master (a35896e) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #507   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            6         6           
  Lines         2200      2208    +8     
=========================================
+ Hits          2200      2208    +8     

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

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