Update .cirrus.yml

.cirrus.yml

@@ -24,7 +24,7 @@ task:
     - flutter upgrade
   create_simulator_script:
     - xcrun simctl list
-    - xcrun simctl create Flutter-iPhone com.apple.CoreSimulator.SimDeviceType.iPhone-X com.apple.CoreSimulator.SimRuntime.iOS-13-4 | xargs xcrun simctl boot
+    - xcrun simctl create Flutter-iPhone com.apple.CoreSimulator.SimDeviceType.iPhone-X com.apple.CoreSimulator.SimRuntime.iOS-13-3 | xargs xcrun simctl boot
   build_script:
     - cd example
     - flutter build ios --no-codesign