Fix Typo

Summary:
* This PR fixes a typo for the NetInfo docs page
Closes https://github.com/facebook/react-native/pull/937
Github Author: Mike Wilcox <mwilcox56@gmail.com>

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

Examples/UIExplorer/NetInfoExample.js

@@ -131,12 +131,12 @@ exports.description = 'Monitor network status';
 exports.examples = [
   {
     title: 'NetInfo.isConnected',
-    description: 'Asyncronously load and observe connectivity',
+    description: 'Asynchronously load and observe connectivity',
     render(): ReactElement { return <IsConnected />; }
   },
   {
     title: 'NetInfo.reachabilityIOS',
-    description: 'Asyncronously load and observe iOS reachability',
+    description: 'Asynchronously load and observe iOS reachability',
     render(): ReactElement { return <ReachabilityCurrent />; }
   },
   {

Libraries/Network/NetInfo.js

@@ -34,7 +34,7 @@ type ReachabilityStateIOS = $Enum<{
  *
  * ### reachabilityIOS
  *
- * Asyncronously determine if the device is online and on a cellular network.
+ * Asynchronously determine if the device is online and on a cellular network.
  *
  * - `none` - device is offline
  * - `wifi` - device is online and connected via wifi, or is the iOS simulator
@@ -60,7 +60,7 @@ type ReachabilityStateIOS = $Enum<{
  *
  * ### isConnected
  *
- * Available on all platforms. Asyncronously fetch a boolean to determine
+ * Available on all platforms. Asynchronously fetch a boolean to determine
  * internet connectivity.
  *
  * ```