sort-comp rule: fix bug affecting instance-methods group

Regarding this issue:

    jsx-eslint#599
    sort-comp: Consider separating static fields & instance fields into separate groups

and this PR, released in v7.6.0:

    jsx-eslint#1470
    Add instance-methods and instance-variables to sort-comp.

there's a bug in the implementation of the `instance-methods` group.

Class instance methods can be declared in two different ways:

    class Main extends React.Component {

        // MethodDefinition -> FunctionExpression
        foo() {}

        // ClassProperty -> ArrowFunctionExpression
        bar = () => {}

    }

Using the `babel-eslint` parser, if a class instance method is
declared as a `FunctionExpression`, then the parent AST node is
a `MethodDefinition`, but the `sort-comp` rule is expecting the
parent node to be a `ClassProperty`, which is wrong.

lib/rules/sort-comp.js

@@ -384,10 +384,11 @@ module.exports = {
           node.value.type !== 'ArrowFunctionExpression' &&
           node.value.type !== 'FunctionExpression',
         instanceMethod: !node.static &&
-          node.type === 'ClassProperty' &&
           node.value &&
-          (node.value.type === 'ArrowFunctionExpression' ||
-            node.value.type === 'FunctionExpression'),
+          (
+            (node.type === 'ClassProperty' && node.value.type === 'ArrowFunctionExpression') ||
+            (node.type === 'MethodDefinition' && node.value.type === 'FunctionExpression')
+          ),
         typeAnnotation: !!node.typeAnnotation && node.value === null
       }));
 

tests/lib/rules/sort-comp.js

@@ -315,8 +315,8 @@ ruleTester.run('sort-comp', rule, {
     code: [
       'class Hello extends React.Component {',
       '  foo = () => {}',
-      '  constructor() {}',
       '  classMethod() {}',
+      '  constructor() {}',
       '  static bar = () => {}',
       '  render() {',
       '    return <div>{this.props.text}</div>;',
@@ -573,7 +573,7 @@ ruleTester.run('sort-comp', rule, {
       '}'
     ].join('\n'),
     parser: 'babel-eslint',
-    errors: [{message: 'foo should be placed before constructor'}],
+    errors: [{message: 'classMethod should be placed before constructor'}],
     options: [{
       order: [
         'instance-methods',