renumber motor questions to drop non-existent 8.4

Author: yukomunakata

content/1-simulations/index.md

@@ -70,13 +70,13 @@ Note: no sims for chapter 5
 
 ## Chapter 8: Motor Control and Reinforcement Learning
 
-* [bg](https://compcogneuro.org/sims/ch8/bg): Action selection / gating and reinforcement learning in the basal ganglia. (Questions **8.1 -- 8.4**)
+* [bg](https://compcogneuro.org/sims/ch8/bg): Action selection / gating and reinforcement learning in the basal ganglia. (Questions **8.1 -- 8.3**)
 
-* [rl](https://compcogneuro.org/sims/ch8/rl): Pavlovian Conditioning using Temporal Differences Reinforcement Learning. (Questions **8.5 -- 8.6**)
+* [rl](https://compcogneuro.org/sims/ch8/rl): Pavlovian Conditioning using Temporal Differences Reinforcement Learning. (Questions **8.4 -- 8.5**)
 
-* `pvlv`: Pavlovian Conditioning with the PVLV model (Questions **8.7 -- 8.9**)  **NOT YET AVAIL!**
+* `pvlv`: Pavlovian Conditioning with the PVLV model (Questions **8.6 -- 8.8**)  **NOT YET AVAIL!**
 
-* `cereb`: Cerebellum role in motor learning, learning from errors. (Questions **8.10 -- 8.11**) **NOT YET AVAIL!**
+* `cereb`: Cerebellum role in motor learning, learning from errors. (Questions **8.9 -- 8.10**) **NOT YET AVAIL!**
 
 ## Chapter 9: Executive Function