Custom screen grabber does not work if `screenshot` plugin not installed.

[Vinay Shukla]

The custom screen grabber should take screenshot even if the screenshot plugin is not installed.

Steps to replicate

• Create a gauge ruby project
• add a failing step
• Add custom screen grabber
• uninstall screenshot
• Change the gauge_plugin_url (or else screenshot plugin will get installed as a required plugin before execution)
• Run gauge specs.
• See the report does not contain any screenshot

[Vinay Shukla]

The fix should be available in nightly >= 29-05-2018