RTL ScrollableTabBar support

Author: Hazem El-Sisy

ScrollableTabBar.js

@@ -8,6 +8,7 @@ const {
   Text,
   Platform,
   Dimensions,
+  I18nManager
 } = ReactNative;
 const Button = require('./Button');
 
@@ -157,10 +158,18 @@ const ScrollableTabBar = React.createClass({
       bottom: 0,
     };
 
-    const dynamicTabUnderline = {
-      left: this.state._leftTabUnderline,
-      width: this.state._widthTabUnderline,
-    };
+    const dynamicTabUnderline = {};
+      if(I18nManager.isRTL){
+        dynamicTabUnderline = {
+          right: this.state._leftTabUnderline,
+          width: this.state._widthTabUnderline,
+        };
+      }else{
+        dynamicTabUnderline = {
+          left: this.state._leftTabUnderline,
+          width: this.state._widthTabUnderline,
+        };
+      }
 
     return <View
       style={[styles.container, {backgroundColor: this.props.backgroundColor, }, this.props.style, ]}