Don't treat warnings as errors when building documentation in Xcode

AppledocSettings.plist

@@ -24,5 +24,7 @@
 	<true/>
 	<key>--logformat</key>
 	<string>xcode</string>
+	<key>--exit-threshold</key>
+	<integer>2</integer>
 </dict>
 </plist>