webproxy: T4468: Fix regex for squidguard source-group

[sever-sever]

Change Summary

Fix regex for webproxy squidguard source-group

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

• https://phabricator.vyos.net/T4468

Component(s) name

webproxy

Proposed changes

How to test

Before fix:

vyos@r14# set service webproxy url-filtering squidguard source-group fdsf

  
  
  URL-filter source-group cannot start with a number!
  Value validation failed
  Set failed

After fix:

vyos@r14# set service webproxy url-filtering squidguard source-group fdsf
[edit]
vyos@r14#

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly