Simplify registry resolution

lib/resolve/npm.js

@@ -2,7 +2,7 @@ var join = require('path').join
 var url = require('url')
 var enc = global.encodeURIComponent
 var got = require('../got')
-var registryFor = require('../registry_for')
+var registryUrl = require('registry-url')
 
 /**
  * Resolves a package in the NPM registry. Done as part of `install()`.
@@ -73,5 +73,5 @@ function toUri (pkg) {
     }
   }
 
-  return url.resolve(registryFor(pkg.name), uri)
+  return url.resolve(registryUrl(pkg.scope), uri)
 }