Update electrsd to v0.15

Cargo.toml

@@ -96,7 +96,7 @@ test-md-docs = ["electrum"]
 lazy_static = "1.4"
 env_logger = "0.7"
 clap = "2.33"
-electrsd = { version= "0.13", features = ["trigger", "bitcoind_22_0"] }
+electrsd = { version= "0.15", features = ["trigger", "bitcoind_22_0"] }
 
 [[example]]
 name = "address_validator"

src/testutils/blockchain_tests.rs

@@ -320,7 +320,7 @@ impl Default for TestClient {
     fn default() -> Self {
         let bitcoind_exe = env::var("BITCOIND_EXE")
             .ok()
-            .or(bitcoind::downloaded_exe_path())
+            .or(bitcoind::downloaded_exe_path().ok())
             .expect(
                 "you should provide env var BITCOIND_EXE or specifiy a bitcoind version feature",
             );