fix(gtfs.yml): add more currency types for fares

[landonreed]

Checklist

• Appropriate branch selected (all PRs must first be merged to dev before they can be merged to master)
• Any modified or new methods or classes have helpful JSDoc and code is thoroughly commented
• The description lists all applicable issues this PR seeks to resolve
• The description lists any configuration setting(s) that differ from the default settings
• All tests and CI builds passing

Description

fixes #550 by adding top currencies traded in world (and major North American currency types).

[evansiroky]

We should add all possible currency types while we're at it. I think it'd be useful to create some kind of script that can automatically output all of these values. Perhaps we can use the currency-codes package as a data source.

[landonreed]

Yea, perhaps you're right @evansiroky.

[binh-dam-ibigroup]

Instead of keying them in manually, can that be retrieved from some other source?

[landonreed]

Actually, I'm not really sure including all of them is warranted @evansiroky and @binh-dam-ibigroup. Having hundreds of values really just clutters the dropdown immensely. Sure, specifying some obscure currency is valid, but if our primary users of the system are North American transit agencies, does it really help to have "Platinum" as a currency type in here?

[binh-dam-ibigroup]

I agree with @landonreed, it's fine to key in a few like in this PR, but it doesn't make sense to key in everything, especially if we just copy from some other place.

[evansiroky]

I'm still a fan of allowing all possible values. The GTFS spec is clear that any ISO 4217 currency code is a valid value. Since we're making software that produces GTFS feeds I don't think it makes sense to exclude valid possible values especially when most values can easily be hidden in a react-select combobox. Go ahead and overrule me if you like though.

[landonreed]

@evansiroky, how do you propose we hide the values with react-select? I'm open to the idea. Feel free to jump on and add commits to #566.

[evansiroky]

Approving for now, but #566 is on my backburner and should be implemented eventually.