Fix Money deprecation warning with :rounding_mode
Fix Money deprecation warning with :rounding_mode

This removes the deprecation warning:

```
[WARNING] The default rounding mode will change from `ROUND_HALF_EVEN`
to `ROUND_HALF_UP` in the next major release. Set it explicitly using
`Money.rounding_mode=` to avoid potential problems.
```

by specifying the default rounding mode at boot time so that it's only
set once for the whole app. See
https://github.com/RubyMoney/money#rounding for details.

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