fix(middleware): use cjs syntax

[pi0]

It is better using CommonJS for module exports to avoid mixing esm/cjs syntaxes in node_modules

resolves #235

[codecov]

Codecov Report

Merging #236 (2c4ffe3) into master (ed76e04) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #236   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            3         3           
  Lines           45        45           
  Branches         9         9           
=========================================
  Hits            45        45           

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