Add Amount.scale

Author: Chris Clark

src/js/ripple/amount.js

@@ -1,4 +1,4 @@
- 'use strict';
+'use strict';
 
 // Represent Ripple amounts and currencies.
 // - Numbers in hex are big-endian.
@@ -156,6 +156,10 @@ Amount.prototype.multiply = function(multiplicand) {
   return this._copy(this._value.times(multiplyBy));
 };
 
+Amount.prototype.scale = function(scaleFactor) {
+  return this._copy(this._value.times(scaleFactor));
+};
+
 Amount.prototype.divide = function(divisor) {
   var divisorAmount = Amount.from_json(divisor);
   if (!this.is_valid()) {