JSON-RPC: transaction: Represent R and S as RpcQuantityHex (#166)

Problem: Go-ethereum client cannot unmarshall json it receives from Ganache's
response to 'eth_getBlockByHash' request.

Best Known Cause: Go-etherum client interprets R and S as quantities, not data
( as evidenced by big.Int type )
(https://github.com/ethereum/go-ethereum/blob/master/core/types/transaction.go#L54)

Temporary solution: Encode R and S as RPC quantity, not data.

Justification: At the moment, it is easier to customize Ganache than to propose
changes to Go-etherum client. Moreover, it appears strange for the Ethereum
JSON RPC Specification to treat R and S as data, not quantities: after all, R
and S and integer-like objects in the context of the elliptic curve
cryptography, i.e. they admit operations such as addition, subtraction,
modulus, etc.

Proposal for long-term solution: From remarks above, it appears most natural to
change the Ethereum JSON RPC Specification to treat R and S as quantities and
change Ganache accordingly.

lib/utils/to.js

@@ -47,7 +47,7 @@ module.exports = {
 
   _rpcQuantityHexString: function(val) {
     val = this.hex(val);
-    // remove all zeroes leading zeros, `0+`, from the hex-encoded value
+    // remove all leading zeros, `0+`, from the hex-encoded value
     // This doesn't remove the last 0 which would be captured by `(.+?)`
     val = val.replace(/^(?:0x)(?:0+(.+?))?$/, "0x$1");
     return val;

lib/utils/transaction.js

@@ -300,8 +300,8 @@ module.exports = class Transaction extends EthereumJsTransaction {
       gasPrice: to.rpcQuantityHexString(this.gasPrice),
       input: to.rpcDataHexString(this.data),
       v: to.nullableRpcQuantityHexString(this.v),
-      r: to.nullableRpcDataHexString(this.r),
-      s: to.nullableRpcDataHexString(this.s)
+      r: to.nullableRpcQuantityHexString(this.r),
+      s: to.nullableRpcQuantityHexString(this.s)
     };
 
     return resultJSON;