RFR: 1578: Skara can't parse shenandoah jdk8u versions like 'shenandoah8u332'

[Erik Joelsson]

When configuring the notify bot for SKARA-1574, I discovered that Skara fails to parse the fixversion of the shenandoah-jdk8u repo. This patch fixes that. 

It seems to me that there is little point in keeping a complete list of valid prefixes in the Skara source code, so instead of adding another explicit string like 'openjdk' or 'openjfx', I made the regexp accept any string of lower case letters as prefix for XuY type version strings.

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Commit messages:
 - Fix comment
 - Fix comment
 - SKARA-1578

Changes: https://git.openjdk.org/skara/pull/1368/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1368&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-1578
  Stats: 5 lines in 2 files changed: 2 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/skara/pull/1368.diff
  Fetch: git fetch https://git.openjdk.org/skara pull/1368/head:pull/1368

PR: https://git.openjdk.org/skara/pull/1368