Clear cache in some specefic instances

[circlecube]

Is your feature request related to a problem? Please describe.
The plugin versioncache should auto clear in a couple instances.

• When a user clicks the "check again" link on the /wp-admin/update-core.php page, which points to: /wp-admin/update-core.php?force-check=1.
• When the plugin updates successfully: this would meet the case that there has been an update and another in the cached time (currently six hours). Currently, if you update in this instance you have to wait until the cache expires before the next update is found. Not perfect, but if you update, it should check to make sure there's not another subsequent update immediately.