Docs: fix spelling and typos on VictorOps page

Why is this change being made?

The VictorOps page (https://about.gitlab.com/devops-tools/victorops/) had multiple spelling and usage errors. This commit corrects them and applies a couple of additional style fixes.

Does this MR meet the acceptance criteria?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what