fix(*): fix issue with mainScreen no longer a function in Xcode 8

Author: Merott

src/plugin.ios.ts

@@ -48,7 +48,7 @@ export class PDFView extends common.PDFView {
   }
 
   private init() {
-    this.ios = new UIWebView(UIScreen.mainScreen().bounds);
+    this.ios = new UIWebView(this.mainScreen.bounds);
     this.delegate = PDFViewDelegate.initWithOwner(new WeakRef(this));
 
     this.ios.autoresizingMask =
@@ -57,6 +57,12 @@ export class PDFView extends common.PDFView {
 
     this.ios.scalesPageToFit = true;
   }
+
+  private get mainScreen() {
+    return typeof UIScreen.mainScreen === 'function' ?
+      UIScreen.mainScreen() :  // xCode 7 and below
+      UIScreen.mainScreen;     // xCode 8+
+  }
 }
 
 class PDFViewDelegate extends NSObject implements UIWebViewDelegate {
@@ -73,4 +79,4 @@ class PDFViewDelegate extends NSObject implements UIWebViewDelegate {
   }
 
   private owner: WeakRef<PDFView>;
-}
+}