minor: sendtoaddress documents the wrong default for the seventh parameter

[howard-stearns]

https://github.com/ElementsProject/elementsbp-api-reference/blob/master/api.md#sendtoaddress documents a seventh parameter for "whether to allow unblinded outputs".

The parameter works correctly (I think), but it appears to default to true, while the documentation says it it defaults to false.

[instagibbs]

Thank you, I'll open an issue on the documentation-side

[howard-stearns]

coolio. thanks.