feat(ui): add Bar component

app/components/UI/Bar.js

@@ -0,0 +1,16 @@
+import React from 'react'
+import { Box } from 'rebass'
+
+/**
+ * @render react
+ * @name Bar
+ * @example
+ * <Bar />
+ */
+class Bar extends React.PureComponent {
+  render() {
+    return <Box width={1} bg="white" css={{ height: '1px' }} {...this.props} as="hr" />
+  }
+}
+
+export default Bar

stories/components/bar.stories.js

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+import React from 'react'
+import { storiesOf } from '@storybook/react'
+import Bar from 'components/UI/Bar'
+
+storiesOf('Components.Bar', module).add('bar', () => <Bar />)

test/unit/components/UI/Bar.spec.js

@@ -0,0 +1,10 @@
+import React from 'react'
+import Bar from 'components/UI/Bar'
+import renderer from 'react-test-renderer'
+
+describe('component.UI.Bar', () => {
+  it('should render correctly', () => {
+    const tree = renderer.create(<Bar />).toJSON()
+    expect(tree).toMatchSnapshot()
+  })
+})

test/unit/components/UI/__snapshots__/Bar.spec.js.snap

@@ -0,0 +1,14 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`component.UI.Bar should render correctly 1`] = `
+.c0 {
+  width: 100%;
+  background-color: white;
+  height: 1px;
+}
+
+<hr
+  className="c0"
+  width={1}
+/>
+`;