encoding/json: added docs to UnsupportedValueError
Added godoc to UnsupportedValueError.
Change-Id: I5fc13bac0b6e14b3a6eba27c9d3331ff5c5269aa
GitHub-Last-Rev:
516cd7a92903e1048caa4d560abf5d66339e5a8f
GitHub-Pull-Request: golang/go#41364
Reviewed-on: https://go-review.googlesource.com/c/go/+/254540
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Trust: Daniel Martí <mvdan@mvdan.cc>
Trust: Heschi Kreinick <heschi@google.com>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Go Bot <gobot@golang.org>