Fix spellcheck issue

[mwestphal]

Fix spellcheck issue, you may want to add a spellcheck action on your CI.

Detected in f3d-app/f3d#1034

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Pull request checklist

Read the Contribution Guidelines for detailed information.

• Changes are described in the pull request, or an existing issue is referenced.
• The test suite compiles and runs without error.
• Code coverage is 100%. Test cases can be added by editing the test suite.
• The source code is amalgamated; that is, after making changes to the sources in the include/nlohmann directory, run make amalgamate to create the single-header files single_include/nlohmann/json.hpp and single_include/nlohmann/json_fwd.hpp. The whole process is described here.

[coveralls]

coverage: 100.0%. remained the same when pulling 59bd76c on mwestphal:fix_spellcheck into 35c0b3e on nlohmann:develop.

[nlohmann]

Looks good to me.

[nlohmann]

Thanks!