cargo: loosen the error-chain dependency

Cargo.toml

@@ -21,7 +21,7 @@ serde_derive = "~0.9"
 url = "^1.4"
 
 chrono = { version = "~0.3", features = ["serde"] }
-error-chain = "~0.9"
+error-chain = ">= 0.9, < 0.11"
 serde = "~0.9"
 serde_json = "~0.9"