JDK 9 RFR of JDK-8136738: InputStream documentation for IOException in skip() is unclear or incorrect

[Brian Burkhalter]

Please review at your convenience this API doc-only change:

Issue:	https://bugs.openjdk.java.net/browse/JDK-8136738
Patch:	http://cr.openjdk.java.net/~bpb/8136738/webrev.00/

Summary:

Try to make the specification of InputStream.skip() slightly more precise.

Thanks,

Brian