typo

Fixes #69.

R=r
https://golang.org/cl/152082

doc/effective_go.html

@@ -1467,7 +1467,7 @@ func (p *ByteSlice) Write(data []byte) (n int, err os.Error) {
 	slice := *p;
 	// Again as above.
 	*p = slice;
-	return len(data), nil)
+	return len(data), nil;
 }
 </pre>
 <p>