RFR 8077036: swing docs: fix some tidy warnings

[alexander stepanov]

Hello,

Could you please review the following fix
http://cr.openjdk.java.net/~avstepan/8077036/webrev.00/
for
https://bugs.openjdk.java.net/browse/JDK-8077036

Just some minor docs cleanup; no other code affected.

Thanks,
Alexander