Enable rand crate by default.

See dalek-cryptography#139.

Cargo.toml

@@ -47,7 +47,7 @@ harness = false
 # required-features = ["batch"]
 
 [features]
-default = ["std", "u64_backend"]
+default = ["std", "rand", "u64_backend"]
 std = ["curve25519-dalek/std", "ed25519/std", "serde_crate/std", "sha2/std", "rand/std"]
 alloc = ["curve25519-dalek/alloc", "rand/alloc", "zeroize/alloc"]
 nightly = ["curve25519-dalek/nightly"]