RFR: 8272915: (doc) package-info typo in extLink

[Bradford Wetmore]

Added missing @.  Link now works.

-------------

Commit messages:
 - 8272915: (doc) package-info typo in extLink

Changes: https://git.openjdk.java.net/jdk/pull/5284/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5284&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8272915
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5284.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5284/head:pull/5284

PR: https://git.openjdk.java.net/jdk/pull/5284