RFR: Update link to OCA.

[Stuart Marks]

The old link redirected here, but it's probably best to have a direct link.

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Commit messages:
 - Update link to OCA.

Changes: https://git.openjdk.java.net/guide/pull/65/files
 Webrev: https://webrevs.openjdk.java.net/?repo=guide&pr=65&range=00
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/guide/pull/65.diff
  Fetch: git fetch https://git.openjdk.java.net/guide pull/65/head:pull/65

PR: https://git.openjdk.java.net/guide/pull/65