refactor: use core-em instead of core-emotion

Author: gregberge

docs/basics/Emotion.mdx

@@ -10,16 +10,16 @@ By default Smooth UI uses [styled-components](http://styled-components.com/), bu
 
 ### Installation
 
-Install `@smooth-ui/core-emotion`, `react-emotion` and `emotion-theming` from npm:
+Install `@smooth-ui/core-em`, `react-emotion` and `emotion-theming` from npm:
 
-`npm install @smooth-ui/core-emotion react-emotion emotion-theming`
+`npm install @smooth-ui/core-em react-emotion emotion-theming`
 
 ### Usage
 
-Import components from `@smooth-ui/core-emotion`.
+Import components from `@smooth-ui/core-em`.
 
 ```js
-import { Button } from '@smooth-ui/core-emotion'
+import { Button } from '@smooth-ui/core-em'
 
 const App = () => (
   <Button variant="primary">Hello world!</Button>
@@ -34,7 +34,7 @@ Even if it is not required, is recommended to apply a global normalize before us
 
 ```js
 import { injectGlobal } from 'react-emotion'
-import { globalStyle } from '@smooth-ui/core-sc'
+import { globalStyle } from '@smooth-ui/core-em'
 
 injectGlobal`${globalStyle}`
 ```

scripts/pkg.js

@@ -3,7 +3,7 @@ const pkg = require('../package.json')
 const { STYLED_ENGINE } = process.env
 
 const packageNames = {
-  emotion: '@smooth-ui/core-emotion',
+  emotion: '@smooth-ui/core-em',
   'styled-components': '@smooth-ui/core-sc',
 }