Update validator of no-confusing-arrow for ESLint 6

Fixes #90. Instead of adding ESLint version knowledge to the validators,
I went with the simpler approach of letting the validator consider the
ESLint 6 default value to always be the default. This means that ESLint
<=5 users now must explicitly set `{allowParens: false}`.

README.md

@@ -373,29 +373,30 @@ For example, the rule could warn about this line:
 var x = a => 1 ? 2 : 3;
 ```
 
-By default, ESLint suggests switching to an explicit return:
-
-```js
-var x = a => { return 1 ? 2 : 3; };
-```
-
-That causes no problems with Prettier.
-
-With `{allowParens: true}`, adding parentheses is also considered a valid way to
-avoid the arrow confusion:
+With `{allowParens: true}` (the default since ESLint 6.0.0), adding
+parentheses is considered a valid way to avoid the arrow confusion:
 
 ```js
 var x = a => (1 ? 2 : 3);
 ```
 
-While Prettier keeps thoses parentheses, it removes them if the line is long
+While Prettier keeps those parentheses, it removes them if the line is long
 enough to introduce a line break:
 
 ```js
 EnterpriseCalculator.prototype.calculateImportantNumbers = inputNumber =>
   1 ? 2 : 3;
 ```
 
+With `{allowParens: false}`, ESLint instead suggests switching to an explicit
+return:
+
+```js
+var x = a => { return 1 ? 2 : 3; };
+```
+
+That causes no problems with Prettier.
+
 If you like this rule, it can be used just fine with Prettier as long as the
 `allowParens` option is off.
 
@@ -404,11 +405,18 @@ Example ESLint configuration:
 ```json
 {
   "rules": {
-    "no-confusing-arrow": "error"
+    "no-confusing-arrow": ["error", { "allowParens": false }]
   }
 }
 ```
 
+(Note: The CLI helper tool considers `{allowParens: true}` to be the default,
+which is the case since ESLint 6.0.0. The tool will produce a warning if you
+use the default even if you use an older version of ESLint. It doesn’t hurt
+to explicitly set `{allowParens: false}` even though it is technically
+redundant. This way you are prepared for a future ESLint upgrade and the CLI
+tool can be kept simple.)
+
 ### [no-mixed-operators]
 
 **This rule requires special attention when writing code.**

bin/validators.js

@@ -32,7 +32,7 @@ module.exports = {
 
   "no-confusing-arrow"(options) {
     if (options.length === 0) {
-      return true;
+      return false;
     }
 
     const firstOption = options[0];

test/validators.test.js

@@ -56,8 +56,8 @@ rule("lines-around-comment", {
 });
 
 rule("no-confusing-arrow", {
-  valid: [[], [{ allowParens: false }], [null]],
-  invalid: [[{ allowParens: true }]]
+  valid: [[{ allowParens: false }], [null]],
+  invalid: [[], [{ allowParens: true }]]
 });
 
 rule("vue/html-self-closing", {