Fix issue when days-before-close is more than days-before-stale

[luketomlinson]

Changes

When we introduced #717, we inadvertently introduced a bug that would occur when days-before-close > days-before-stale.

Example:

days-before-stale: 0 and days-before-close: 30

Every issue should be stale in this scenario and the stale label would be applied as expected. The problem was is that the action would look back 30 days and ALWAYS see an update and immediately remove the stale label.

My changes change the logic that can potentially "un-stale" an issue. Rather than check for an update in the last days-before-close days (e.g. 30), I check if the update occurred AFTER the stale date. This is subtle, but caused big issues for actions when days-before-close > days-before-stale

Context

fixes #774

[benwells]

LGTM 👍