ui-stats.c: fix warning on 32-bit

gcc 6.3.0-18 on Debian stable emits the following warning,
despite uintptr_t and "unsigned long" having the same size:

> ../ui-stats.c: In function ‘print_authors’:
> ../ui-stats.c:340:18: warning: format ‘%lu’ expects argument of type ‘long unsigned int’, but argument 2 has type ‘unsigned int’ [-Wformat=]
>      htmlf("<td>%lu</td>", (uintptr_t)date->util);
>                   ^

1 files changed, 4 insertions, 2 deletions

diff --git a/ui-stats.c b/ui-stats.c
index 7acd358..d7c4c97 100644
--- a/ui-stats.c
+++ b/ui-stats.c
@@ -337,8 +337,10 @@ static void print_authors(struct string_list *authors, int top,
                         if (!date)
                                 html("<td>0</td>");
                         else {
-                                htmlf("<td>%lu</td>", (uintptr_t)date->util);
-                                total += (uintptr_t)date->util;
+                                uintptr_t util = (uintptr_t)date->util;
+
+                                htmlf("<td>%"PRIuPTR"</td>", util);
+                                total += util;
                         }
                 }
                 htmlf("<td class='sum'>%ld</td></tr>", total);