[BUG][python] Fix PEP8 E111 issue in rest.mustache

[swimmwatch]

Hello! I fixed PEP8 E111 issue in rest.mustache.

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package 
  ./bin/generate-samples.sh
  ./bin/utils/export_docs_generators.sh
  

  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
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  @taxpon (2017/07) @frol (2017/07) @mbohlool (2017/07) @cbornet (2017/09) @kenjones-cisco (2017/11) @tomplus (2018/10) @arun-nalla (2019/11) @spacether (2019/11)

[spacether]

Hey there, I think that you are targeting the wrong branch. Are you meaning to merge it into the openapi-generator source repo master branch? If so please change the branch that your PR is targeting.

[swimmwatch]

@spacether, sorry. I messed up the forked rep and the origin rep. I created issue and PR and they are closed and merged.