RFR: 7903356: jtreg Def.gmk fails to find tidy

[Leonid Mesnik]

Added missing space.

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Commit messages:
 - fix

Changes: https://git.openjdk.org/jtreg/pull/132/files
 Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=132&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903356
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jtreg/pull/132.diff
  Fetch: git fetch https://git.openjdk.org/jtreg pull/132/head:pull/132

PR: https://git.openjdk.org/jtreg/pull/132