fix eslint error

Author: hengkx

examples/gradient-circle.js

@@ -3,42 +3,40 @@ import React, { Component } from 'react';
 import ReactDOM from 'react-dom';
 import { Circle } from 'rc-progress';
 
-class Example extends Component {
-  render() {
-    const circleContainerStyle = {
-      width: '250px',
-      height: '250px',
-      display: 'inline-block',
-    };
-    return (
-      <div>
-        <h3>Circle Progress {90}%</h3>
-        <div style={circleContainerStyle}>
-          <Circle
-            percent={90}
-            strokeWidth="6"
-            strokeLinecap="round"
-            strokeColor={{
-              '0%': '#108ee9',
-              '100%': '#87d068',
-            }}
-          />
-        </div>
-        <h3>Circle Progress {100}%</h3>
-        <div style={circleContainerStyle}>
-          <Circle
-            percent={100}
-            strokeWidth="6"
-            strokeLinecap="round"
-            strokeColor={{
-              '100%': '#87d068',
-              '0%': '#108ee9',
-            }}
-          />
-        </div>
+const Example = () => {
+  const circleContainerStyle = {
+    width: '250px',
+    height: '250px',
+    display: 'inline-block',
+  };
+  return (
+    <div>
+      <h3>Circle Progress {90}%</h3>
+      <div style={circleContainerStyle}>
+        <Circle
+          percent={90}
+          strokeWidth="6"
+          strokeLinecap="round"
+          strokeColor={{
+            '0%': '#108ee9',
+            '100%': '#87d068',
+          }}
+        />
       </div>
-    );
-  }
-}
+      <h3>Circle Progress {100}%</h3>
+      <div style={circleContainerStyle}>
+        <Circle
+          percent={100}
+          strokeWidth="6"
+          strokeLinecap="round"
+          strokeColor={{
+            '100%': '#87d068',
+            '0%': '#108ee9',
+          }}
+        />
+      </div>
+    </div>
+  );
+};
 
 ReactDOM.render(<Example />, document.getElementById('__react-content'));