godoc/static: re-add "or" function call to package.html template

It was removed unintentionally in CL 101295, where the intention was
to remove the (eq $.Dirname "/src") condition.

Updates golang/go#35812

Change-Id: I1591ed221f0d510fb1ffa51a3ecd48d8327fdfbb
Reviewed-on: https://go-review.googlesource.com/c/tools/+/208661
Reviewed-by: Agniva De Sarker <agniva.quicksilver@gmail.com>

godoc/static/package.html

@@ -263,7 +263,7 @@
 				<th class="pkg-synopsis">Synopsis</th>
 			</tr>
 
-			{{if not ((eq $.Dirname "/src/cmd") $.DirFlat)}}
+			{{if not (or (eq $.Dirname "/src/cmd") $.DirFlat)}}
 			<tr>
 				<td colspan="2"><a href="..">..</a></td>
 			</tr>