Implement check of newer versions in the list command.

Also:
- Fix some errors not being emitted when a command failed.
- Update semver module; no need to check .valid against null.

lib/commands/uninstall.js

@@ -24,7 +24,8 @@ function uninstall(names, options, config) {
     project.uninstall(names, options)
     .then(function (installed) {
         emitter.emit('end', installed);
-    }, function (error) {
+    })
+    .fail(function (error) {
         emitter.emit('error', error);
     });