In the sigmoid function there is -theta(Transpose)*X and while taking the derivation it would be -Xj not Xj and the equation reverses.
Problem with derivation
There will be two negative signs in the derivation of sigmoid function, so hence they will compensate, otherwise send the pic of your derivation where you are struck so that we can help you.
Hope this cleared your doubt. 
I hope I’ve cleared your doubt. I ask you to please rate your experience here
Your feedback is very important. It helps us improve our platform and hence provide you
the learning experience you deserve.
On the off chance, you still have some questions or not find the answers satisfactory, you may reopen
the doubt.