Bump min macOS version to 10.9.

This will be required once Xamarin.Mac starts using mono/2018-08.

Author: rolfbjarne

src/framework/Info.plist

@@ -23,7 +23,7 @@
 	<key>CFBundleVersion</key>
 	<string>1</string>
 	<key>LSMinimumSystemVersion</key>
-	<string>10.8</string>
+	<string>10.9</string>
 	<key>NSHumanReadableCopyright</key>
 	<string>(C) Xamarin 2015</string>
 	<key>NSMainNibFile</key>