doc/go1.3.txt: unicode upgrade to 6.3.0

LGTM=mpvl
R=mpvl
CC=golang-codereviews
https://golang.org/cl/65550044

doc/go1.3.txt

@@ -7,3 +7,4 @@ testing: diagnose buggy tests that panic(nil) (CL 55780043)
 testing: add b.RunParallel function (CL 57270043)
 misc/benchcmp has been replaced by go tool benchcmp (CL 47980043)
 cmd/go, go/build: support .m files (CL 60590044)
+unicode: upgrade from Unicode 6.2.0 to 6.3.0 (CL 65400044)