Fix typo in geojson help.
Fix typo in geojson help.

btahir/topojson,AlpinHologramm/topojson,maxogden/topojson,mbostock/topojson,ststeiger/topojson,ongerit/topojson,hcxiong/topojson,lyhpcha/topojson,studiowangfei/topojson,youprofit/topojson,whoinlee/topojson,koshlan/topojson,tsl3su/WorldMap_Choropleth