Fixed code highlighting
minor #4215 Fixed code highlighting (WouterJ)

This PR was merged into the 2.3 branch.

Discussion
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Fixed code highlighting

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

 > Double quoted strings are the only scalar style capable of expressing arbitrary strings, by using “\” escape sequences.
 > - http://yaml.org/spec/1.1/#id904245

`\w` and `\d` are invalid escape sequences in Yaml, causing the Yaml highlighter to fail.

Commits
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f4b5dc6 Fixed code highlighting