Fix sample configuration file linting issues.

[karlism]

Before:

$ yamllint-3 jiralert.yml
  2:1       warning  missing document start "---"  (document-start)
  38:18     error    too many spaces inside brackets  (brackets)
  38:31     error    too many spaces inside brackets  (brackets)
  46:27     error    too many spaces inside braces  (braces)
  46:42     error    too many spaces inside braces  (braces)

After:

$ yamllint-3 jiralert.yml