feat(casper): update casper version during ghost update

refs #225
- delete old casper version and replace with new one on update
- short term solution

lib/commands/update.js

@@ -97,6 +97,16 @@ module.exports.execute = function execute(version, options) {
     }, {
         title: 'Linking things',
         task: tasks.link
+    }, {
+        title: 'Installing new version of Casper',
+        task: (ctx) => {
+            let casperPath = path.join(process.cwd(), 'content', 'themes', 'casper');
+
+            return fs.remove(casperPath).then(() => fs.move(
+                path.join(ctx.installPath, 'content', 'themes', 'casper'),
+                casperPath
+            ));
+        }
     }, {
         title: 'Restarting Ghost',
         task: () => startCommand.execute.call(this, {quiet: true})