Fixed build problem on Cirrus-CI (brianegan#133)

* Fixed problem where available simulator runtime versions differed across
macos instances

Author: mmcc007

.cirrus.yml

@@ -87,9 +87,9 @@ task:
     - xcrun simctl list devicetypes
     - xcrun simctl list runtimes
     # create simulator
-    - udid=$(xcrun simctl create "iPhone X" com.apple.CoreSimulator.SimDeviceType.iPhone-X com.apple.CoreSimulator.SimRuntime.iOS-12-1)
+    - udid=$(xcrun simctl create "iPhone X" com.apple.CoreSimulator.SimDeviceType.iPhone-X com.apple.CoreSimulator.SimRuntime.iOS-12-0)
     # boot simulator
     - xcrun simctl boot $udid
   doctor_script: flutter doctor -v
   devices_script: flutter devices
-  ci_script: ./scripts/ci.sh ./$app_arch || ./scripts/ci.sh ./$app_arch
+  ci_script: ./scripts/ci.sh ./$app_arch || ./scripts/ci.sh ./$app_arch