Change mojo url to always use mojo:foo instead of mojo://foo

sky/framework/xmlhttprequest.sky

 <import src="/mojo/public/sky/core.sky" as="core" />
 <import src="/mojo/public/sky/unicode.sky" as="unicode" />
 <import src="/mojo/services/public/interfaces/network/network_service.mojom.sky" as="net" />
 <import src="/mojo/services/public/interfaces/network/url_loader.mojom.sky" as="loader" />
 <import src="shell.sky" as="shell" />
 <script>
 function XMLHttpRequest() {
   this.networkService_ = shell.connectToService(
-    "mojo://network_service/", net.NetworkService);
+    "mojo:network_service", net.NetworkService);
   this.request_ = null;
   this.loader_ = null;
   this.responseText = null;
   this.headers_ = new Map();
 };
 
 XMLHttpRequest.prototype.onload = function() { };
 XMLHttpRequest.prototype.onerror = function(error) { };
 
 XMLHttpRequest.prototype.open = function(method, url) {
@@ skipping 26 matching lines @@
       self.responseText = unicode.decodeUtf8String(new Uint8Array(result.buffer));
       self.onload();
     });
   }).catch(function(error) {
     self.onerror(error);
   });
 };
 
 module.exports = XMLHttpRequest;
 </script>