Mark the ignore_missing_submod option as unstable

Author: tanzaku

Configurations.md

@@ -1294,7 +1294,7 @@ Ignore missing submodule error.
 
 - **Default value**: `false`
 - **Possible values**: `true`, `false`
-- **Stable**: Yes
+- **Stable**: No
 
 ## `imports_indent`
 

src/config/mod.rs

@@ -173,7 +173,7 @@ create_config! {
          or they are left with trailing whitespaces";
     ignore: IgnoreList, IgnoreList::default(), false,
         "Skip formatting the specified files and directories";
-    ignore_missing_submod: bool, false, true, "Ignore missing submodule error";
+    ignore_missing_submod: bool, false, false, "Ignore missing submodule error";
 
     // Not user-facing
     verbose: Verbosity, Verbosity::Normal, false, "How much to information to emit to the user";