Bump nim-eth minimum to 0.8.0 (#207)

`TxEip7873` has been removed from nim-eth.

Author: etan-status

web3.nimble

@@ -18,7 +18,7 @@ requires "nim >= 2.0.0"
 requires "chronicles"
 requires "chronos"
 requires "bearssl"
-requires "eth >= 0.7.0"
+requires "eth >= 0.8.0"
 requires "faststreams"
 requires "json_rpc"
 requires "json_serialization"