[Button] Auto import LinearGradient if Expo (#943)

* Warning only for non-expo user

* Auto import LinearGradient on Expo

* Show warning if non-expo user

* Update example

* Update snapshot

src/buttons/Button.js

@@ -21,20 +21,17 @@ const log = () => {
 
 class Button extends Component {
   componentDidMount() {
-    if (
-      this.props.linearGradientProps != null &&
-      this.props.ViewComponent == null
-    ) {
+    const { linearGradientProps, ViewComponent } = this.props;
+    if (linearGradientProps && !global.Expo && !ViewComponent) {
       /* eslint-disable no-console */
       console.error(
-        `You need to pass a ViewComponent to use linearGradientProps !\nExample: ViewComponent={require('expo').LinearGradient}`
+        `You need to pass a ViewComponent to use linearGradientProps !\nExample: ViewComponent={require('react-native-linear-gradient')}`
       );
     }
   }
 
   render() {
     const {
-      ViewComponent,
       TouchableComponent,
       containerStyle,
       onPress,
@@ -50,6 +47,7 @@ class Button extends Component {
       iconContainerStyle,
       iconRight,
       linearGradientProps,
+      ViewComponent = linearGradientProps && global.Expo ? global.Expo.LinearGradient : View,
       ...attributes
     } = this.props;
 
@@ -132,7 +130,6 @@ Button.defaultProps = {
   iconRight: false,
   TouchableComponent:
     Platform.OS === 'ios' ? TouchableOpacity : TouchableNativeFeedback,
-  ViewComponent: View,
   onPress: log,
   clear: false,
   loadingProps: {

src/pricing/__tests__/__snapshots__/PricingCard.js.snap

@@ -131,7 +131,6 @@ exports[`PricingCard component should render with props 1`] = `
     </TextElement>
     <Button
       TouchableComponent={[Function]}
-      ViewComponent={[Function]}
       buttonStyle={
         Array [
           Object {
@@ -283,7 +282,6 @@ exports[`PricingCard component should render without issues 1`] = `
     </TextElement>
     <Button
       TouchableComponent={[Function]}
-      ViewComponent={[Function]}
       buttonStyle={
         Array [
           Object {