Made CHANGELOG formatting more consistent.
Made CHANGELOG formatting more consistent.

We follow a new format starting from 0.28. To avoid confusion
and remove precedents of alternate styles, this cleans up
formatting for previous releases.

Review: https://reviews.apache.org/r/45484/

yuquanshan/customizedMesos,reneploetz/mesos,reneploetz/mesos,jpeach/mesos,reneploetz/mesos,verizonlabs/mesos,gsantovena/mesos,jpeach/mesos,verizonlabs/mesos,Gilbert88/mesos,chhsia0/mesos,yuquanshan/customizedMesos,craimbert/mesos,craimbert/mesos,reneploetz/mesos,abudnik/mesos,neilconway/mesos,andschwa/mesos,asamerh4/mesos,neilconway/mesos,zmalik/mesos,Gilbert88/mesos,verizonlabs/mesos,yuquanshan/customizedMesos,jpeach/mesos,kaysoky/mesos,kaysoky/mesos,verizonlabs/mesos,neilconway/mesos,Aman-Jain-14/customizedMesos,dforsyth/mesos,verizonlabs/mesos,asamerh4/mesos,andschwa/mesos,yuquanshan/customizedMesos,zmalik/mesos,abudnik/mesos,andschwa/mesos,zmalik/mesos,zmalik/mesos,asamerh4/mesos,abudnik/mesos,gsantovena/mesos,dforsyth/mesos,abudnik/mesos,chhsia0/mesos,reneploetz/mesos,kaysoky/mesos,abudnik/mesos,andschwa/mesos,jpeach/mesos,Aman-Jain-14/customizedMesos,zmalik/mesos,Aman-Jain-14/customizedMesos,Gilbert88/mesos,kaysoky/mesos,craimbert/mesos,kaysoky/mesos,asamerh4/mesos,Gilbert88/mesos,chhsia0/mesos,gsantovena/mesos,yuquanshan/customizedMesos,abudnik/mesos,Aman-Jain-14/customizedMesos,kaysoky/mesos,dforsyth/mesos,verizonlabs/mesos,Gilbert88/mesos,yuquanshan/customizedMesos,abudnik/mesos,craimbert/mesos,Gilbert88/mesos,neilconway/mesos,craimbert/mesos,gsantovena/mesos,Aman-Jain-14/customizedMesos,neilconway/mesos,neilconway/mesos,andschwa/mesos,Aman-Jain-14/customizedMesos,chhsia0/mesos,chhsia0/mesos,verizonlabs/mesos,dforsyth/mesos,gsantovena/mesos,neilconway/mesos,asamerh4/mesos,jpeach/mesos,jpeach/mesos,gsantovena/mesos,yuquanshan/customizedMesos,reneploetz/mesos,gsantovena/mesos,dforsyth/mesos,zmalik/mesos,craimbert/mesos,andschwa/mesos,asamerh4/mesos,chhsia0/mesos,craimbert/mesos,zmalik/mesos,dforsyth/mesos,kaysoky/mesos,asamerh4/mesos,dforsyth/mesos,Aman-Jain-14/customizedMesos,jpeach/mesos,andschwa/mesos,chhsia0/mesos,reneploetz/mesos,Gilbert88/mesos