Fix linting errors in jira.md

Fix linting errors in https://docs.gitlab.com/ee/user/project/import/jira.html

36:64  error  Avoid using future tense: "will be". Use present tense instead.     gitlab.FutureTense
79:10  error  Avoid using future tense: "will be". Use present tense instead.     gitlab.FutureTense
91:28  error  Avoid using future tense: "you'll see". Use present tense instead.  gitlab.FutureTense

If you'd like to work on this issue, mention @msedlakjakubowski in a comment. Then, in your merge request's description, paste this issue's URL so they become linked.

Edited Dec 01, 2020 by Marcin Sedlak-Jakubowski