docs: update example code of Limitations

[Gavin-Gong]

just adjust example code by webpack doc

for previous code
if you use webpack --env development command in webpack 5.3,
then env will be
{ WEBPACK_SERVE: true, development: true }, instead of development or production

[codecov-io]

Codecov Report

Merging #180 (1bb6dab) into develop (28cfdbd) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #180   +/-   ##
========================================
  Coverage    99.14%   99.14%           
========================================
  Files            6        6           
  Lines          233      233           
  Branches        64       64           
========================================
  Hits           231      231           
  Misses           2        2           

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[bebraw]

Thanks! Sorry for the late merge (busy with other things).