Update to SCALE 1.2.0 (#5113)

This updates `parity-scale-codec` to `1.2.0`, which includes multiple
performance improvements and a fix that bounds the capacity of a vector
at decoding.

substrate/utils/frame/rpc/system/Cargo.toml

@@ -10,7 +10,7 @@ description = "FRAME's system exposed over Substrate RPC"
 
 [dependencies]
 sc-client = { version = "0.8.0-alpha.2", path = "../../../../client/" }
-codec = { package = "parity-scale-codec", version = "1.0.0" }
+codec = { package = "parity-scale-codec", version = "1.2.0" }
 futures = "0.3.1"
 jsonrpc-core = "14.0.3"
 jsonrpc-core-client = "14.0.3"