Fixed bug with transit time priors for more than one planet

[ssagear]

Hello,

I came across the same error as in Issue #81 that occurs when fitting more than one planet with TTVs. In setting the lightcurve prior dict, when a transit time prior is detected, 'parametrization' is only set to 'T' for the last planet in the system. I changed the indexing in line 570 so 'parametrization' = 'T' is set for all planets with transit time priors. After doing this, fitting multi-planet systems with transit time priors seems to proceed as expected.

Best, Sheila