Bump Doppler instance count to 60
Bump Doppler instance count to 60

Doppler instance count should track 50 percent of Diego-cell count
(58.5) rounded to 60 as is required to be divisible by 3 to evenly
distribute across AZs.

alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf