stylelint: Move .stylelintrc to stylelint.config.js.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

docs/testing/linters.md

@@ -215,7 +215,7 @@ clean those files up eventually.
 
 Zulip uses [stylelint](https://github.com/stylelint/stylelint) to lint
 its CSS; see our
-[configuration](https://github.com/zulip/zulip/blob/master/.stylelintrc)
+[configuration](https://github.com/zulip/zulip/blob/master/stylelint.config.js)
 for the rules we currently enforce.
 
 #### Shell scripts

stylelint.config.js

@@ -1,6 +1,8 @@
-{
-    "rules": {
-        # Stylistic rules for CSS.
+"use strict";
+
+module.exports = {
+    rules: {
+        // Stylistic rules for CSS.
         "function-comma-space-after": "always",
         "function-comma-space-before": "never",
         "function-max-empty-lines": 0,
@@ -58,10 +60,10 @@
         "at-rule-semicolon-space-before": "never",
 
         "comment-whitespace-inside": "always",
-        "indentation": 4,
+        indentation: 4,
 
-        # Limit language features
+        // Limit language features
         "color-no-hex": true,
         "color-named": "never",
-    }
-}
+    },
+};

tools/lint

@@ -51,7 +51,7 @@ def run() -> None:
     linter_config.external_linter('css', ['node', 'node_modules/.bin/stylelint'], ['css', 'scss'],
                                   fix_arg='--fix',
                                   description="Standard CSS style and formatting linter "
-                                  "(config: .stylelintrc)")
+                                  "(config: stylelint.config.js)")
     linter_config.external_linter('eslint', ['node', 'node_modules/.bin/eslint',
                                              '--quiet', '--cache', '--ext', '.js,.ts'], ['js', 'ts'],
                                   fix_arg='--fix',