fix: optional chaining syntax in dist module

[agriffis]

Set the esbuild target so that optional chaining is transformed in the output module.

Partial fix for #265 and #270

[netlify[bot]]

👷 Deploy request for xstyled accepted.

Name	Link
🔨 Latest commit	5f0bf2b2565d74547fe46f6c83be92e4a0cc5b95
🔍 Latest deploy log	https://app.netlify.com/sites/xstyled/deploys/60b621f513b62b0008b6ea06

[codecov[bot]]

Codecov Report

Merging #271 (5f0bf2b) into main (2a59389) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #271   +/-   ##
=======================================
  Coverage   92.73%   92.73%           
=======================================
  Files          60       60           
  Lines        1252     1252           
  Branches      244      244           
=======================================
  Hits         1161     1161           
  Misses         91       91           

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