Update LegendType with game enum change

[Archomeda]

The enum LegendType is hardcoded to start with 13, but the game update of June 9th, 2020 incremented all those values with 1, causing Legend1 to start at 14.

It's currently not actually used by the chat links, even though I had planned it (but probably forgot about them). It's used as an additional input parameter for the API legends endpoint, which uses a string instead. So the enum change isn't that impactful internally in Gw2Sharp, but might be if dependents actually use it.