RFR: GTest docs moved

[Jesper Wilhelmsson]

Updated links to GTest Docs.

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Commit messages:
 - GTest docs moved

Changes: https://git.openjdk.org/guide/pull/138/files
  Webrev: https://webrevs.openjdk.org/?repo=guide&pr=138&range=00
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/guide/pull/138.diff
  Fetch: git fetch https://git.openjdk.org/guide.git pull/138/head:pull/138

PR: https://git.openjdk.org/guide/pull/138