[paymentrequest] CurrencyAmount description has exponent sign wrong (#39)

Compare [the description](https://github.com/WICG/paymentrequest/blob/gh-pages/specs/paymentrequest.html#L525-L527):

> A CurrencyAmount dictionary is used to supply monetary amounts with known precision using base-10. The value of the amount is mantissa * 10 ^ exponent. The following fields must be supplied for a CurrencyAmount to be valid:

to [the example given](https://github.com/WICG/paymentrequest/blob/gh-pages/specs/paymentrequest.html#L525-L527):

> The following example shows how to represent US$55.00.

```
EXAMPLE 6
{
  "currencyCode": "USD",
  "mantissa": 5500,
  "exponent": 2
}
```

If the value was mantissa * 10 ^ exponent, the value would be 550000 not 55.00.

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Reply to this email directly or view it on GitHub:
https://github.com/WICG/paymentrequest/issues/39