Fix the description of `params->'progress'`

https://uphold.com/en/developer/api/documentation/#transaction-object

Instead of:
```
In case a transaction is coming in from the outside, how many confirmations have been received.
```
we should have something like:
```
In case of a external transaction (deposit/withdrawal), reflects the progress percentage (between 0.0 and 1.0).
```
