update MapIt data and governors CSV from bin/prepare-data too

[mhl]

For performance in development, and so that we're not internet dependent when running the the Sinatra app, we use local copies of the governors CSV file and the MapIt Area data:

mapit/FED.json
mapit/SEN.json
mapit/STA.json
morph/nigeria-state-governors.csv

It would probably make sense to update these from the bin/prepare-data script, though, since that's already dependent on getting data from the internet. This will mean putting a valid MORPH_API_KEY in the Travis config of shineyoureye-prose so that automated deployments from there can still get the governors data from https://morph.io/everypolitician-scrapers/nigeria-state-governors