RFR: 8285658: Fix two typos in the spec of j.u.random.RandomGenerator

[Raffaello Giulietti]

The spec of the interface `java.util.random.RandomGenerator` is slightly incorrect when it discusses `float` and `double` random values.

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Commit messages:
 - Fix two typos in the spec of j.u.random.RandomGenerator

Changes: https://git.openjdk.java.net/jdk/pull/8404/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8404&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8285658
  Stats: 8 lines in 1 file changed: 1 ins; 0 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8404.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8404/head:pull/8404

PR: https://git.openjdk.java.net/jdk/pull/8404