make config_dev.yml a valid YML file

`%..%` must be wrapped by quotes, or YML file is not valid!
bug #687 make config_dev.yml a valid YML file (jdespatis)

This PR was submitted for the master branch but it was merged into the 2.5 branch instead (closes #687).

Discussion
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make config_dev.yml a valid YML file

`%..%` must be wrapped by quotes, or YML file is not valid!

Commits
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848b095 make config_dev.yml a valid YML file
Merge branch '2.5'

* 2.5:
  make config_dev.yml a valid YML file