Created by: bmordue

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\. If contributing template-only or documentation-only changes which will change sample output, be sure to build the project first.
• Filed the PR against the correct branch: master, 4.1.x, 5.0.x. Default: master.
• Copied the technical committee to review the pull request if your PR is targeting a particular programming language.

Description of the PR

This is a small fix for JSON serialization using sprintf of 'numeric' types in R that is already in swagger-codegen: Relevant issue: https://github.com/swagger-api/swagger-codegen/issues/8531

cc @andypetrella

Note: running the sample generation script ./bin/openapi3/r-petstore.sh has added new files.