Dear Airflow maintainers,

Please accept this PR. I understand that it will not be reviewed until I have checked off all the steps below!

### Opened PR
- [x] Opened a PR on Github


### [JIRA](https://issues.apache.org/jira/browse/AIRFLOW/)
- [ ] My PR addresses the following Airflow JIRA issues:
    - https://issues.apache.org/jira/browse/AIRFLOW-XXX
- [ ] The PR title references the JIRA issues. For example, "[AIRFLOW-1] My Airflow PR"


### Tests
- [ ] My PR adds unit tests
- [ ] __OR__ my PR does not need testing for this extremely good reason:


### Description
- [ ] Here are some details about my PR:
- [ ] Here are screenshots of any UI changes, if appropriate:


### Commits
- [ ] Each commit subject references a JIRA issue. For example, "[AIRFLOW-1] Add new feature"
- [ ] Multiple commits addressing the same JIRA issue have been squashed
- [ ] My commits follow the guidelines from "[How to write a good git commit message](http://chris.beams.io/posts/git-commit/)":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"


Dear Airflow maintainers,

Please accept this PR. I understand that it will not be reviewed until I have checked off all the steps below!


### JIRA
- [ ] My PR addresses the following [Airflow JIRA](https://issues.apache.org/jira/browse/AIRFLOW/) issues and references them in the PR title. For example, "[AIRFLOW-XXX] My Airflow PR"
    - https://issues.apache.org/jira/browse/AIRFLOW-XXX


### Description
- [ ] Here are some details about my PR, including screenshots of any UI changes:


### Tests
- [ ] My PR adds the following unit tests __OR__ does not need testing for this extremely good reason:


### Commits
- [ ] My commits all reference JIRA issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "[How to write a good git commit message](http://chris.beams.io/posts/git-commit/)":
    1. Subject is separated from body by a blank line
    2. Subject is limited to 50 characters
    3. Subject does not end with a period
    4. Subject uses the imperative mood ("add", not "adding")
    5. Body wraps at 72 characters
    6. Body explains "what" and "why", not "how"


Remove reference to actual Airflow issue
[AIRFLOW-995] Remove reference to actual Airflow issue

Remove example reference to AIRFLOW-[one] because
it confuses merge tools. In addition, simplify
the checkboxes because Github displays how many
of them have been checked off.

Closes #2163 from jlowin/pr-template-2
