code: function extractJsonDataFrom(content) {
      let firstValidIndex = 0;
      for (let index = 0; index <= content.length - 1; index++) {
          const char = content.charAt(index);
          if (char === '[' || char === '{') {
              firstValidIndex = index;
              break;
          }
      }
      return content.substr(firstValidIndex);
  }
docs: Extract the Json data from input content.
  The problem: the 'npm pack --json > output.log' command will run any 'prepublish' script
  defined in the package.json file before executing the npm pack command itself.
  In the context of publish-please, any already-installed publish-please package
  has already a prepublish script:  "prepublish": "publish-please guard"
  this will give the following output:
  > testing-repo@1.3.77 prepublish ...
  > publish-please guard
  [{real ouput of npm pack}]
  
  So the input content may be either a valid json file
  or valid json data prefixed by the result of the prepublish script execution
  @param {string} content