doc: fix minor typo in Go 1 release notes

Fixes #3478.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5986074

doc/go1.html

@@ -1788,7 +1788,7 @@ for full details.
 <td colspan="2"><hr></td>
 </tr>
 <tr><td>Atoui(x)</td> <td>ParseUint(x, 10, 0)§</td></tr>
-<tr><td>Atoi64(x)</td> <td>ParseInt(x, 10, 64)</td></tr>
+<tr><td>Atoui64(x)</td> <td>ParseUint(x, 10, 64)</td></tr>
 <tr>
 <td colspan="2"><hr></td>
 </tr>