Update HISTORY.md

Author: isaacsas

HISTORY.md

@@ -1,9 +1,11 @@
 # Breaking updates and feature summaries across releases
 
 ## JumpProcesses unreleased (master branch)
+
+## 9.3
 - Support for "bounded" `VariableRateJump`s that can be used with the `Coevolve`
  aggregator for faster simulation of jump processes with time-dependent rates.
  In particular, if all `VariableRateJump`s in a pure-jump system are bounded one
  can use `Coevolve` with `SSAStepper` for better performance. See the
  documentation, particularly the first and second tutorials, for details on
- defining and using bounded `VariableRateJump`s.
+ defining and using bounded `VariableRateJump`s.