use cfg! instead of #[cfg] and use semver

Cargo.toml

@@ -69,7 +69,7 @@ test-md-docs = ["electrum"]
 lazy_static = "1.4"
 env_logger = "0.7"
 clap = "2.33"
-electrsd = { version="0.4.0", features = ["trigger"] }
+electrsd = { version="0.4", features = ["trigger"] }
 
 [[example]]
 name = "address_validator"

src/testutils/blockchain_tests.rs

@@ -26,10 +26,7 @@ impl TestClient {
         debug!("launching {} and {}", &bitcoind_exe, &electrs_exe);
         let bitcoind = BitcoinD::new(bitcoind_exe).unwrap();
 
-        #[cfg(feature = "test-esplora")]
-        let http_enabled = true;
-        #[cfg(not(feature = "test-esplora"))]
-        let http_enabled = false;
+        let http_enabled = cfg!(feature = "test-esplora");
 
         let electrsd = ElectrsD::new(electrs_exe, &bitcoind, false, http_enabled).unwrap();