Fix Markdown in .github/ISSUE_TEMPLATE.md

[igorshubovych]

Fixed Markdown to make checkboxes work.

Incorrect

-[ ] item

Correct:

- [ ] item (notice space)

And this is how it looks like:
-[x] incorrect

• correct

See video tutorial about checkboxes.

[codecov-io]

Current coverage is 90.49%

Merging #859 into master will decrease coverage by -1.17% as of 1b33eb8

@@            master    #859   diff @@
======================================
  Files           71      71       
  Stmts         4102    4102       
  Branches       845     845       
  Methods          0       0       
======================================
- Hit           3760    3712    -48
  Partial         10      10       
- Missed         332     380    +48

Review entire Coverage Diff as of 1b33eb8

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[drew-gross]

Thanks! I was wondering why this wasn't working.