Fixed the formatting of the table headers
minor #3900 Fixed the formatting of the table headers (javiereguiluz)

This PR was submitted for the 2.5 branch but it was merged into the 2.3 branch instead (closes #3900).

Discussion
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Fixed the formatting of the table headers

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.5+
| Fixed tickets | -

Commits
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d043f91 Fixed the formatting of the table headers