tool_sleep: typecast to avoid macos compiler warning

tool_sleep.c:54:24: error: implicit conversion loses integer precision:
'long' to '__darwin_suseconds_t' (aka 'int')
[-Werror,-Wshorten-64-to-32]

src/tool_sleep.c

@@ -5,7 +5,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2014, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -51,7 +51,7 @@ void tool_go_sleep(long ms)
   struct timeval timeout;
   timeout.tv_sec = ms / 1000L;
   ms = ms % 1000L;
-  timeout.tv_usec = ms * 1000L;
+  timeout.tv_usec = (int)ms * 1000;
   select(0, NULL,  NULL, NULL, &timeout);
 #endif
 }