add hasIframe property to support iframe on iOS; bump version to 0.3.4

README.md

 ```javascript
 <AutoHeightWebView
     onHeightUpdated={height => console.log(height)},
+    // if page contains iframe on iOS, use a specific script for it
+    hasIframe={true}
     /*
     if set to false may cause some layout issues (width of container not fit for screen) on android
     if set to true may cause some layout issues (smaller font size) on ios

autoHeightWebView/index.ios.js

 
 export default class AutoHeightWebView extends PureComponent {
     static propTypes = {
+        hasIframe: PropTypes.bool,
         source: WebView.propTypes.source,
         onHeightUpdated: PropTypes.func,
         customScript: PropTypes.string,
         if (this.props.enableAnimation) {
             this.opacityAnimatedValue = new Animated.Value(0);
         }
-        const initialScript = props.files ? this.appendFilesToHead(props.files, BaseScript) : BaseScript;
+        const initialScript = props.files ? this.appendFilesToHead(props.files, props.hasIframe ? IframeBaseScript : BaseScript) : props.hasIframe ? IframeBaseScript : BaseScript;
         this.state = {
             height: 0,
             script: initialScript
     }
 
     componentWillReceiveProps(nextProps) {
-        let currentScript = BaseScript;
+        let currentScript = nextProps.hasIframe ? IframeBaseScript : BaseScript;
         if (nextProps.files) {
-            currentScript = this.appendFilesToHead(nextProps.files, BaseScript);
+            currentScript = this.appendFilesToHead(nextProps.files, nextProps.hasIframe ? IframeBaseScript : BaseScript);
         }
         this.setState({ script: currentScript });
     }
         window.addEventListener('load', updateHeight);
         window.addEventListener('resize', updateHeight);
     } ());
+    `;
+
+const IframeBaseScript =
+    `
+    ; 
+    (function () {
+        var i = 0;
+        var height = 0;
+        function updateHeight() {
+            if(document.body.offsetHeight !== height) {
+                height = document.body.firstChild.clientHeight;
+                document.title = document.body.firstChild.clientHeight;
+                window.location.hash = ++i;
+            }
+        }
+        updateHeight();
+        window.addEventListener('load', updateHeight);
+        window.addEventListener('resize', updateHeight);
+    } ());
     `;

demo/yarn.lock

     ws "^2.0.3"
 
 react-native-autoheight-webview@../:
-  version "0.3.3"
+  version "0.3.4"
   dependencies:
     immutable "^3.8.1"
     prop-types "^15.5.10"

package.json

 {
   "name": "react-native-autoheight-webview",
-  "version": "0.3.3",
+  "version": "0.3.4",
   "description": "An auto height webview for React Native",
   "main": "autoHeightWebView",
   "files": [
     "immutable": "^3.8.1",
     "prop-types": "^15.5.10"
   }
-}
+}