Update Rust crate dropshot to 0.16.0

Author: oxide-renovate[bot]

Cargo.toml

@@ -57,7 +57,7 @@ colored = "2"
 csv = "1.3"
 curl = "0.4"
 display-error-chain = "0.2"
-dropshot = "0.15.1"
+dropshot = "0.16.0"
 expectorate = "1"
 futures = "0.3"
 http = "1.2.0"