Elliott pointed out that we output "unlimited" instead of "infinity", so
accept that as input. (And that I screwed up the test.)
diff --git a/toys/posix/ulimit.c b/toys/posix/ulimit.c
index b4d8e94..0aedd2c 100644
--- a/toys/posix/ulimit.c
+++ b/toys/posix/ulimit.c
@@ -107,7 +107,7 @@
   if (toys.optc) {
     rlim_t val;
 
-    if (tolower(**toys.optargs == 'i')) val = RLIM_INFINITY;
+    if (tolower(**toys.optargs) == 'u') val = RLIM_INFINITY;
     else val = atolx_range(*toys.optargs, 0, LONG_MAX);
 
     if (toys.optflags&FLAG_H) rr.rlim_max = val;