Fixed bad link in secrets.js.template

weather/server/lib/secrets.js.template

 //Template file for secrets.js
 //Duplicate this file and name it 'secrets.js'
 //Replace 'YOUR_API_KEY_HERE' with your Forcast.io API key
-//You can get an API key at https://developer.darksky.net
+//You can get an API key at https://darksky.net/dev/
 //(Dark Sky's API was formerly called Forecast.io)
 Meteor.startup(function () {
   process.env.API_KEY = 'YOUR_API_KEY_HERE';