fix: gpx response not returned correctly

[TheGreatRefrigerator]

the text response from the gpx endpoint was also retrieved through the .json function of the Response object which threw an error as it was not possible to parse the gpx to json.

For gpx it now uses the .text function instead and just returns the gpx result as a string.

[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[codecov-commenter]

Codecov Report

Merging #75 (c9a3865) into main (2504198) will not change coverage. The diff coverage is 100.00%.

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@@           Coverage Diff           @@
##             main      #75   +/-   ##
=======================================
  Coverage   99.09%   99.09%           
=======================================
  Files          15       15           
  Lines         331      331           
  Branches       57       57           
=======================================
  Hits          328      328           
  Misses          3        3           

Files Changed	Coverage Δ
src/OrsBase.js	100.00% <100.00%> (ø)