RFR: Fix typo in HotSpotDiagnostic

[Octavia Togami]

This PR simply fixes a small typo in the error message thrown by `HotSpotDiagnostic#dumpThreads`.

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Commit messages:
 - Fix typo in HotSpotDiagnostic

Changes: https://git.openjdk.java.net/loom/pull/36/files
 Webrev: https://webrevs.openjdk.java.net/?repo=loom&pr=36&range=00
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/loom/pull/36.diff
  Fetch: git fetch https://git.openjdk.java.net/loom pull/36/head:pull/36

PR: https://git.openjdk.java.net/loom/pull/36