Correct misspelled getPrefences() to getPreferences() in file createdvsresolved-gadget.xml

We can't use JIRA's Created vs Resolved gadget in other applications, like Confluence, because someone typo-ed the name of the function in a call to getPreferences().

My PMs reported that this breakage appeared in Confluence after I upgraded our JIRA from 6.3.9 to 7.1.6. When they try to add a JIRA Created vs Resolved gadget to a confluence page, the preview pane is blank and they can't finish the configuration that would allow them to insert the gadget.

With Chrome's developer tools, I found that an error on the page when I chose the gadget and just after the browser tried to render the preview panel in the gadget config screen. The error is "Uncaught ReferenceError: getPrefences is not defined." Which makes perfect sense because the function is named getPrefe*re*nces, not getPrefences

and then looked in the source and at line 372 in file
.../jira-components/jira-plugins/jira-gadgets-plugin/src/main/resources/gadgets/createdvsresolved-gadget.xml

I see this:
var preferences = getPrefences(gadget);
and it should be
var preferences = getPreferences(gadget);

It's missing the crucial "re" sylable.