Add children prop

- Fixes #21

Author: ntkme

index.d.ts

@@ -1,4 +1,8 @@
 import React from 'react'
 import { GitHubButtonProps } from 'github-buttons'
 
-export default class GitHubButton extends React.PureComponent<GitHubButtonProps> {}
+interface ReactGitHubButtonProps extends GitHubButtonProps {
+  children?: React.ReactNode;
+}
+
+export default class GitHubButton extends React.PureComponent<ReactGitHubButtonProps> {}