doc/go_spec: fix a typo

R=nigeltao
CC=golang-dev
https://golang.org/cl/6499075

doc/go_spec.html

 <!--{
 	"Title": "The Go Programming Language Specification",
-	"Subtitle": "Version of August 29, 2012",
+	"Subtitle": "Version of September 4, 2012",
 	"Path": "/ref/spec"
 }-->
 
@@ -383,7 +383,7 @@ a literal <code>a</code>-dieresis, U+00E4, value <code>0xe4</code>.
 </p>
 <p>
 Several backslash escapes allow arbitrary values to be encoded as
-as ASCII text.  There are four ways to represent the integer value
+ASCII text.  There are four ways to represent the integer value
 as a numeric constant: <code>\x</code> followed by exactly two hexadecimal
 digits; <code>\u</code> followed by exactly four hexadecimal digits;
 <code>\U</code> followed by exactly eight hexadecimal digits, and a