download: Add socks support for reqwest-backend

Author: Eduard Miller

Cargo.lock

@@ -20,7 +20,7 @@ url = "2.1"
 curl = { version = "0.4.11", optional = true }
 env_proxy = { version = "0.4.1", optional = true }
 lazy_static = { version = "1.0", optional = true }
-reqwest = { version = "0.10", features = ["blocking", "gzip"], optional = true }
+reqwest = { version = "0.10", features = ["blocking", "gzip", "socks"], optional = true }
 
 [dev-dependencies]
 hyper = { version = "0.13", default-features = false, features = ["tcp"] }