A Drow has 120 ft Darkvision, while a Spider has 30 ft Darkvision. The Druid's Wild Shape ability says this:
Your game statistics are replaced by the statistics of the beast, […]
And it says this about Darkvision:
You retain the benefit of any features from your class, race, or other source and can use them if the new form is physically capable of doing so. However, you can't use any of your Special senses, such as Darkvision, unless your new form also has that sense.
Since the Spider also has Darkvision, the Druid will be able to use Darkvision while Wild Shaped. But will the Darkvision be 30 ft, or 120ft?
You keep the Drow race's range on Darkvision. The rules say you retain your racial features, but can't use special senses unless your new form also has them:
You retain your race's Darkvision, and so you retain Darkvision 120'. If you wild shape into a beast that does not have Darkvision, you can't use your Special Sense but you have still retained it. If you wild shape into a beast that does have Darkvision, though, then you can use it. And since you retained the feature from your race, you use your race-granted version of it, which has the longer range.