[meta] CHANGES entry for Docker refactoring.

CHANGES.md

-# jsCoq 0.15.0 "Go For Your Toad, or Similar"
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+# jsCoq 0.15.1 "Go For Your Toad, or Similar"
+---------------------------------------
 
  - Update to Coq 8.15.1 (@corwin-of-amber)
+ - Stabilized jsCoq SDK Docker image (@corwin-of-amber)
 
 # jsCoq 0.15.0 "Steady State"
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