add redundant features for cargo 1.41 bug

Author: apoelstra

Cargo.toml

@@ -23,8 +23,8 @@ std = ["alloc", "secp256k1-sys/std"]
 # allow use of Secp256k1::new and related API that requires an allocator
 alloc = ["secp256k1-sys/alloc"]
 bitcoin-hashes = ["bitcoin_hashes"] # Feature alias because of the underscore.
-bitcoin-hashes-std = ["std", "bitcoin_hashes/std"]
-rand-std = ["std", "rand/std", "rand/std_rng"]
+bitcoin-hashes-std = ["std", "bitcoin_hashes", "bitcoin_hashes/std"]
+rand-std = ["std", "rand", "rand/std", "rand/std_rng"]
 recovery = ["secp256k1-sys/recovery"]
 lowmemory = ["secp256k1-sys/lowmemory"]
 global-context = ["std"]