RFR: Usign perl instead of sed

[Jesper Wilhelmsson]

It turns out that different common versions of sed behaves differently so the suggestion here is to replace it with
perl.

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Commit messages:
 - Usign perl instead of sed

Changes: https://git.openjdk.java.net/guide/pull/10/files
 Webrev: https://webrevs.openjdk.java.net/guide/10/webrev.00
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/guide/pull/10.diff
  Fetch: git fetch https://git.openjdk.java.net/guide pull/10/head:pull/10

PR: https://git.openjdk.java.net/guide/pull/10