Update validations to reflect office slug
Update validations to reflect office slug

President/Vice-president races are standardized to "President".
I needed to update the slug used in these tests to reflect the
standardized office name.

Addresses #49

datamade/openelections-core,cathydeng/openelections-core,datamade/openelections-core,cathydeng/openelections-core,openelections/openelections-core,openelections/openelections-core