old_contents: #
  # json.py
  # Linter for SublimeLinter3, a code checking framework for Sublime Text 3
  #
  # Written by Aparajita Fishman
  #
  # Project: https://github.com/SublimeLinter/SublimeLinter-contrib-json
  # License: MIT
  #
  
  import json
  
  from SublimeLinter.lint import Linter
  
  
  class JSON(Linter):
      language = 'json'
      cmd = None
      regex = r'^(?P<error>.+):\s*line (?P<line>\d+) column (?P<col>\d+)'
  
      def run(self, cmd, code):
          try:
              json.loads(code)
          except ValueError as err:
              return str(err)
  
          return ''
  
new_contents: #
  # json.py
  # Linter for SublimeLinter3, a code checking framework for Sublime Text 3
  #
  # Written by Aparajita Fishman
  #
  # Project: https://github.com/SublimeLinter/SublimeLinter-contrib-json
  # License: MIT
  #
  
  import json
  
  from SublimeLinter.lint import Linter
  
  
  class JSON(Linter):
      language = 'json'
      cmd = None
      regex = r'^(?P<message>.+):\s*line (?P<line>\d+) column (?P<col>\d+)'
  
      def run(self, cmd, code):
          try:
              json.loads(code)
          except ValueError as err:
              return str(err)
  
          return ''
  
subject: Change capture group name