[Artifacts]: Fix docstring

Author: staticfloat

stdlib/Artifacts/src/Artifacts.jl

@@ -407,7 +407,7 @@ end
 
 """
     artifact_hash(name::String, artifacts_toml::String;
-                  platform::AbstractPlatform = platform_key_abi())
+                  platform::AbstractPlatform = HostPlatform())
 
 Thin wrapper around `artifact_meta()` to return the hash of the specified, platform-
 collapsed artifact.  Returns `nothing` if no mapping can be found.