add funder to possible values for institution type

[smierz]

fixes #25

Status quo

OpenAlex docs for the institution object and its types lists

Possible values are: Education, Healthcare, Company, Archive, Nonprofit, Government, Facility, and Other

while the linked ROR types consist of

Allowed types are education, funder, healthcare, company, archive, nonprofit, government, facility, and other.

--> In OpenAlex docs the type "funder" is missing

Proposed changes

This PR adds "funder" to the list of possible values for institution type.