Fix Payment source & destination types (#870)

Payment `source` and `destination` are defined as intersection types, `Adjustment & MaxAdjustment` and  `Adjustment & MinAdjustment` respectively. But they should be union types instead. This problem was introduced during js to ts conversion.

Fixes #866

src/transaction/payment.ts

@@ -10,8 +10,8 @@ import {Amount, Adjustment, MaxAdjustment,
 
 
   export type Payment = {
-  source: Adjustment & MaxAdjustment,
-  destination: Adjustment & MinAdjustment,
+  source: Adjustment | MaxAdjustment,
+  destination: Adjustment | MinAdjustment,
   paths?: string,
   memos?: Array<Memo>,
   // A 256-bit hash that can be used to identify a particular payment
@@ -74,8 +74,8 @@ function createPaymentTransaction(address: string, paymentArgument: Payment
     throw new ValidationError('address must match payment.source.address')
   }
 
-  if ((payment.source.maxAmount && payment.destination.minAmount) ||
-      (payment.source.amount && payment.destination.amount)) {
+  if (((<MaxAdjustment>payment.source).maxAmount && (<MinAdjustment>payment.destination).minAmount) ||
+      ((<Adjustment>payment.source).amount && (<Adjustment>payment.destination).amount)) {
     throw new ValidationError('payment must specify either (source.maxAmount '
       + 'and destination.amount) or (source.amount and destination.minAmount)')
   }
@@ -86,9 +86,9 @@ function createPaymentTransaction(address: string, paymentArgument: Payment
   // send the whole source amount, so we set the destination amount to the
   // maximum possible amount. otherwise it's possible that the destination
   // cap could be hit before the source cap.
-  const amount = payment.destination.minAmount && !isXRPToXRPPayment(payment) ?
-    createMaximalAmount(payment.destination.minAmount) :
-    (payment.destination.amount || payment.destination.minAmount)
+  const amount = (<MinAdjustment>payment.destination).minAmount && !isXRPToXRPPayment(payment) ?
+    createMaximalAmount((<MinAdjustment>payment.destination).minAmount) :
+    ((<Adjustment>payment.destination).amount || (<MinAdjustment>payment.destination).minAmount)
 
   const txJSON: any = {
     TransactionType: 'Payment',
@@ -122,15 +122,15 @@ function createPaymentTransaction(address: string, paymentArgument: Payment
     // https://github.com/ripple/rippled/commit/
     //  c522ffa6db2648f1d8a987843e7feabf1a0b7de8/
     if (payment.allowPartialPayment === true
-        || payment.destination.minAmount !== undefined) {
+        || (<MinAdjustment>payment.destination).minAmount !== undefined) {
       txJSON.Flags |= paymentFlags.PartialPayment
     }
 
     txJSON.SendMax = toRippledAmount(
-      payment.source.maxAmount || payment.source.amount)
+      (<MaxAdjustment>payment.source).maxAmount || (<Adjustment>payment.source).amount)
 
-    if (payment.destination.minAmount !== undefined) {
-      txJSON.DeliverMin = toRippledAmount(payment.destination.minAmount)
+    if ((<MinAdjustment>payment.destination).minAmount !== undefined) {
+      txJSON.DeliverMin = toRippledAmount((<MinAdjustment>payment.destination).minAmount)
     }
 
     if (payment.paths !== undefined) {