Update Rust crate config to 0.15

Author: renovate[bot]

Cargo.toml

@@ -10,7 +10,7 @@ license = "MIT"
 edition = "2021"
 
 [dependencies]
-config = { version="0.11", default-features=false, features=["yaml"] }
+config = { version="0.15", default-features=false, features=["yaml"] }
 diesel = { version="1.4", default-features=false, features=["sqlite"] }
 serde = { version="1.0", default-features=false, features=["derive", "std"] }
 serde_json = "1.0"