Fix typos in array::erase docs

[grisumbras]

Fix #620

[codecov]

Codecov Report

Merging #623 (1c18230) into develop (1265dbe) will not change coverage.
The diff coverage is n/a.

❗ Current head 1c18230 differs from pull request most recent head c5edf02. Consider uploading reports for the commit c5edf02 to get more accurate results

@@           Coverage Diff            @@
##           develop     #623   +/-   ##
========================================
  Coverage    99.05%   99.05%           
========================================
  Files           68       68           
  Lines         6119     6119           
========================================
  Hits          6061     6061           
  Misses          58       58           

Impacted Files	Coverage Δ
include/boost/json/array.hpp	100.00% <ø> (ø)

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[cppalliance-bot]

Benchmark test results. More info at https://benchmark.cppalliance.org/jsonbenchmarks-pullrequests/623/pullrequest.html

[cppalliance-bot]

Benchmark test results. More info at https://benchmark.cppalliance.org/jsonbenchmarks-pullrequests/623/pullrequest.html