Rename --use_hex to --hex

This is much more common on unix systems, and I end up typing it by
accident most of the time.  And it is shorter too.

Change-Id: I8e4bbc186a8a82c7546d74e161c145825f0c4c0f
Signed-off-by: Austin Schuh <austin.linux@gmail.com>
diff --git a/aos/aos_cli_utils.cc b/aos/aos_cli_utils.cc
index b930af5..a4ea95e 100644
--- a/aos/aos_cli_utils.cc
+++ b/aos/aos_cli_utils.cc
@@ -228,7 +228,7 @@
   aos::FlatbufferToJson(
       builder, channel->schema(), static_cast<const uint8_t *>(context.data),
       {options.pretty, static_cast<size_t>(options.max_vector_size),
-       options.pretty_max, options.use_hex});
+       options.pretty_max, options.hex});
 
   if (options.json) {
     std::cout << "{";