Add m3.medium to EC2 instance types
Add m3.medium to EC2 instance types

This is the lowest `m3` family instance type with ephemeral storage.
azavea/raster-foundry,kdeloach/raster-foundry,kdeloach/raster-foundry,kdeloach/raster-foundry,aaronxsu/raster-foundry,azavea/raster-foundry,azavea/raster-foundry,raster-foundry/raster-foundry,raster-foundry/raster-foundry,aaronxsu/raster-foundry,azavea/raster-foundry,aaronxsu/raster-foundry,raster-foundry/raster-foundry,azavea/raster-foundry,kdeloach/raster-foundry,aaronxsu/raster-foundry,kdeloach/raster-foundry