Modify kpod diff --json to --format json

We want all kpod subcommands to use the formats code to output
formats like json.  Altering kpod diff --json to kpod diff --format json
like the kpod images command.

Signed-off-by: baude <bbaude@redhat.com>

completions/bash/kpod

@@ -35,10 +35,10 @@ _kpod_info() {
     local boolean_options="
      --help
      -h
-     --json
      --debug
      "
     local options_with_args="
+    --format
   "
 
     local all_options="$options_with_args $boolean_options"