fresh zoning data pull, updated ordinance links, dependency bumps

[derekeder]

• Pulled fresh zoning data: esri2geojson http://gisapps.cityofchicago.org/arcgis/rest/services/ExternalApps/Zoning/MapServer/1 chicago-zoning.geojson Closes #18
• Updated link to AM Legal zoning code: http://library.amlegal.com/nxt/gateway.dll/Illinois/chicagozoning/chicagozoningordinanceandlanduseordinanc?f=templates$fn=default.htm$3.0$vid=amlegal:chicagozoning_il' target='_blank'><i class='fa fa-external-link
• Upgraded to Ruby 2.6.2 and Jekyll 4.0
• Link highlighting syntax fix to appease Jekyll 4.0