Pin de-dependency versions for zip and base64ct to work with MSRV 1.57

Author: notmandatory

Cargo.toml

@@ -28,6 +28,10 @@ tokio = { version = "1.20.1", features = ["full"] }
 electrsd = { version = "0.22.0", features = ["legacy", "esplora_a33e97e1", "bitcoind_22_0"] }
 electrum-client = "0.12.0"
 lazy_static = "1.4.0"
+# zip versions after 0.6.3 don't work with our MSRV 1.57.0
+zip = "=0.6.3"
+# base64ct versions at 1.6.0 and higher have MSRV 1.60.0
+base64ct = "<1.6.0"
 
 [features]
 default = ["blocking", "async", "async-https"]