Fix linting errors in process-geojson
Fix linting errors in process-geojson

There were two linting errors that were each the only violations of the
rule in question and seemed better to fix than allow:
@typescript-eslint/restrict-plus-operands,
"Operands of '+' operation must either be both strings or both numbers"
and @typescript-eslint/require-await,
"Async method 'readSmallGeoJson' has no 'await' expression"

PublicMapping/DistrictBuilder,PublicMapping/DistrictBuilder,PublicMapping/DistrictBuilder,PublicMapping/DistrictBuilder,PublicMapping/DistrictBuilder