Set Android targetSDK to 26

Samples/XamlUIBasics/cs/AppUIBasics.Droid/Properties/AndroidManifest.xml

@@ -1,5 +1,9 @@
 <?xml version="1.0" encoding="utf-8"?>
-<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.nventive.xamlcontrolsgallery" android:versionCode="35" android:versionName="1.0" android:installLocation="auto">
-	<uses-sdk android:minSdkVersion="21" />
+<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
+					package="com.nventive.xamlcontrolsgallery" 
+					android:versionCode="35" 
+					android:versionName="1.0" 
+					android:installLocation="auto">
+	<uses-sdk android:minSdkVersion="21" android:targetSdkVersion="26" />
 	<application android:label="XAML Controls Gallery"></application>
 </manifest>