Expose secp256k1 'rand' feature flag

By exposing this, we can use the 'rand' dependency of secp256k1
in a project that only depends on rust-bitcoin without having to
add a separate dependency in order to activate the feature flag.

Cargo.toml

@@ -18,6 +18,7 @@ path = "src/lib.rs"
 fuzztarget = ["secp256k1/fuzztarget", "bitcoin_hashes/fuzztarget"]
 unstable = []
 use-serde = ["serde", "bitcoin_hashes/serde"]
+rand = ["secp256k1/rand"]
 
 [dependencies]
 bech32 = "0.7.1"

contrib/test.sh

@@ -1,6 +1,6 @@
 #!/bin/sh -ex
 
-FEATURES="bitcoinconsensus use-serde"
+FEATURES="bitcoinconsensus use-serde rand"
 
 if [ "$DO_COV" = true ]
 then