How to create a seamless looping animation, without noticing when the loop occurs?

Unity 5.6

I am trying to create a very simple rotation animation for a 2d object. Its z coordinate changes from 0 to -359 in one loop. at the end of each loop however, the animation slows down and then starts ramping up speed. How can I make it so that the animation stops slowing down and the looping occurs smoothly and seamlessly.

Edit the curves. Right now the curves are slow in / slow out. Instead you want a constant or normalized or linear curve.