Fixed chronos link in documentation.
Fixed chronos link in documentation.

The previous link 'airbnb/chronos' is just a mirrow of 'mesos/airbnb'.

Review: https://reviews.apache.org/r/48787/

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