RFR: 8253492: Miss comma after second copyright year in FDBigInteger.java

[Yumin Qi]

In patch for jdk-8253208, a comma missed after copyright year in
src/java.base/share/classes/jdk/internal/math/FDBigInteger.java. Also changed "@return" to "Returns" in the comment for
CDS.getRandomSeedForDumping to keep consistent with others.

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Commit messages:
 - 8253492: Miss comma after second copyright year in FDBigInteger.java

Changes: https://git.openjdk.java.net/jdk/pull/306/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=306&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253492
  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/306.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/306/head:pull/306

PR: https://git.openjdk.java.net/jdk/pull/306