Fix grammatical error in documentation

[kemonprogrammer]

It could also be "There are times..."

• I've followed the contributing guidelines to the best of my understanding
• I've read and understood the contributing guidelines
• (I've formatted my code according to Natron's code style)
• I've searched the pull requests tracker to ensure that this PR is not a duplicate

PR Description

What type of PR is this? (Check one of the boxes below)

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (non-breaking change which does not add functionality nor fixes a bug but improves Natron in some way)
• Breaking change (fix or feature that would cause existing functionality to change)
• My change requires a change to the documentation
  • I have updated the documentation accordingly

What does this pull request do?

I noticed it, and wanted to fix it

Have you tested your changes (if applicable)? If so, how?

Yes

Futher details of this pull request

Link: https://natron.readthedocs.io/en/rb-2.5/guide/tutorials-svgworkflow.html