[amber-docs] RFR: Fixing syntax in example

[David Alayachew]

Missing a parentheses

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Commit messages:
 - Fixing syntax in example

Changes: https://git.openjdk.org/amber-docs/pull/20/files
 Webrev: https://webrevs.openjdk.org/?repo=amber-docs&pr=20&range=00
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/amber-docs/pull/20.diff
  Fetch: git fetch https://git.openjdk.org/amber-docs.git pull/20/head:pull/20

PR: https://git.openjdk.org/amber-docs/pull/20