Typo in the releases part of contributor-guide

Typo of "ensure" ("esnure) should be fixed:
The third period of a release is focusing on finishing the implementation and testing of new functionality added during the release. You need to esnure to add new tests in Tempest and have documentation covered as well before the third milestone. During this phase the core review team can choose to focus on higher priority features only. They make their decision about priorities either at the PTG or soon after, some time before the first milestone of a release.