CompatHelper: bump compat for AbstractPPL to 0.13 for package docs, (keep existing compat)

Author: CompatHelper Julia

docs/Project.toml

@@ -14,7 +14,7 @@ MCMCChains = "c7f686f2-ff18-58e9-bc7b-31028e88f75d"
 StableRNGs = "860ef19b-820b-49d6-a774-d7a799459cd3"
 
 [compat]
-AbstractPPL = "0.11, 0.12"
+AbstractPPL = "0.11, 0.12, 0.13"
 Accessors = "0.1"
 DataStructures = "0.18"
 Distributions = "0.25"