title: IPHONEOS_DEPLOYMENT_TARGET is set to 8.0 Xcode 12 (Flutter)
body: <p>I run my Flutter project in Android Studio, pod installation goes well but Xcode build fails at the end every time like 20/30 steps first of complete the whole build.
  The weird fact is that Android Studio says :</p>
  <pre><code>Command PhaseScriptExecution failed with a nonzero exit code
      note: Using new build system
      note: Building targets in parallel
      note: Planning build
      note: Constructing build description
  warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99. (in target 'GoogleDataTransport' from project 'Pods')
      warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99. (in target 'path_provider' from project 'Pods')
      warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99. (in target 'nanopb' from project 'Pods')
      warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99. (in target 'BoringSSL-GRPC' from project 'Pods')
      warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99. (in target 'AppAuth' from project 'Pods')
      warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99. (in target 'GoogleUtilities' from project 'Pods')
      warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99. (in target 'GTMAppAuth' from project 'Pods')
      warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99. (in target 'gRPC-C++' from project 'Pods')
      warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99. (in target 'google_sign_in' from project 'Pods')
      warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99. (in target 'FirebaseCoreDiagnostics' from project 'Pods')
      warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99. (in target 'FirebaseCore' from project 'Pods')
      warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99. (in target 'FirebaseFirestore' from project 'Pods')
      warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99. (in target 'FirebaseAuth' from project 'Pods')
      warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99. (in target 'firebase_core' from project 'Pods')
      warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99. (in target 'firebase_auth' from project 'Pods')
      warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99. (in target 'cloud_firestore' from project 'Pods')
      warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99. (in target 'gRPC-Core' from project 'Pods')
      warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99. (in target 'Firebase' from project 'Pods')
      warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99. (in target 'gRPC-C++-gRPCCertificates-Cpp' from project 'Pods')
      warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99. (in target 'GoogleSignIn' from project 'Pods')
      warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99. (in target 'leveldb-library' from project 'Pods')
      warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99. (in target 'Flutter' from project 'Pods')
      warning: The iOS Simulator deployment target 'IPHONEOS_DEPLOYMENT_TARGET' is set to 8.0, but the range of supported deployment target versions is 9.0 to 14.2.99. (in target 'abseil' from project 'Pods')
  </code></pre>
  <p>But when I open the workspace with Xcode I see that my target in Runner has <code>iOS deployment target 14.0</code> so I don't understand, it should be set to 14 but actually it's 8.
  Flutter generated <code>Podfile</code>, <code>Podfile.lock</code> and <code>Pods</code> through <code>flutter run</code> I prefer to let Flutter handle Pod generation and installation without using <code>pod init</code>, <code>pod install</code> or editing <code>Podfile</code>.</p>