Add Section 18.9 - No spaces inside parentheses

See #593

README.md

@@ -1551,6 +1551,29 @@ Other Style Guides
     }
     ```
 
+  - [18.9](#18.9) <a name='18.9'></a> Do not add spaces inside parentheses.
+
+    ```javascript
+    // bad
+    function bar( foo ) {
+      return foo;
+    }
+
+    // good
+    function bar(foo) {
+      return foo;
+    }
+
+    // bad
+    if ( foo ) {
+      console.log(foo);
+    }
+
+    // good
+    if (foo) {
+      console.log(foo);
+    }
+    ```
 
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packages/eslint-config-airbnb/rules/style.js

@@ -96,8 +96,8 @@ module.exports = {
     'space-before-blocks': 2,
     // require or disallow space before function opening parenthesis
     'space-before-function-paren': [2, 'never'],
-    // require or disallow spaces inside parentheses
-    'space-in-parens': 0,
+    // disallow spaces inside parentheses
+    'space-in-parens': [2, 'never'],
     // require spaces around operators
     'space-infix-ops': 2,
     // require a space after return, throw, and case