RFR: 8253066: typo in Stream.mapMulti

[Stuart Marks]

A simple typo fix.

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Commit messages:
 - fix typo in Stream.mapMulti

Changes: https://git.openjdk.java.net/jdk/pull/137/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=137&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253066
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/137.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/137/head:pull/137

PR: https://git.openjdk.java.net/jdk/pull/137