spec: libraries and implementation are now at Unicode 6.3

LGTM=gri
R=gri
CC=golang-codereviews
https://golang.org/cl/68760043

doc/go_spec.html

@@ -120,7 +120,7 @@ unicode_digit  = /* a Unicode code point classified as "Decimal Digit" */ .
 </pre>
 
 <p>
-In <a href="http://www.unicode.org/versions/Unicode6.2.0/">The Unicode Standard 6.2</a>,
+In <a href="http://www.unicode.org/versions/Unicode6.3.0/">The Unicode Standard 6.3</a>,
 Section 4.5 "General Category"
 defines a set of character categories.  Go treats
 those characters in category Lu, Ll, Lt, Lm, or Lo as Unicode letters,
@@ -5683,7 +5683,7 @@ package and may be relative to a repository of installed packages.
 <p>
 Implementation restriction: A compiler may restrict ImportPaths to
 non-empty strings using only characters belonging to
-<a href="http://www.unicode.org/versions/Unicode6.2.0/">Unicode's</a>
+<a href="http://www.unicode.org/versions/Unicode6.3.0/">Unicode's</a>
 L, M, N, P, and S general categories (the Graphic characters without
 spaces) and may also exclude the characters
 <code>!"#$%&amp;'()*,:;&lt;=&gt;?[\]^`{|}</code>