Fix WebView automaticallyAdjustContentInsets error

Summary:
WebView component's automaticallyAdjustContentInsets prop should be type BOOL. Fixes facebook#251.
Closes facebook#314
Github Author: Jordanna Kwok <jordannakwok@gmail.com>

Test Plan: Imported from GitHub, without a `Test Plan:` line.

React/Views/RCTWebViewManager.m

@@ -24,7 +24,7 @@ - (UIView *)view
 RCT_REMAP_VIEW_PROPERTY(url, URL, NSURL);
 RCT_REMAP_VIEW_PROPERTY(html, HTML, NSString);
 RCT_EXPORT_VIEW_PROPERTY(contentInset, UIEdgeInsets);
-RCT_EXPORT_VIEW_PROPERTY(automaticallyAdjustContentInsets, UIEdgeInsets);
+RCT_EXPORT_VIEW_PROPERTY(automaticallyAdjustContentInsets, BOOL);
 RCT_EXPORT_VIEW_PROPERTY(shouldInjectAJAXHandler, BOOL);
 
 - (NSDictionary *)constantsToExport