Changed "Contributors" to "Core Maintainers" sections and updated to reflect current roster.
Changed "Contributors" to "Core Maintainers" sections and updated to reflect current roster.

testem/testem,johanneswuerbach/testem,Addepar/testem,bradleylandis/testem,johanneswuerbach/testem,paulot/testem,johanneswuerbach/testem,fotinakis/testem,fotinakis/testem,Addepar/testem,paulot/testem,fotinakis/testem,testem/testem,Addepar/testem,paulot/testem,testem/testem,bradleylandis/testem,Addepar/testem,bradleylandis/testem