title: Flutter iOS build fail on running pod install
body: <p>I'm trying to make a flutter plugin, so I created a plugin by steps provided on <a href="https://flutter.dev/docs/development/packages-and-plugins/developing-packages" rel="noreferrer">https://flutter.dev/docs/development/packages-and-plugins/developing-packages</a>. I'm getting an error when I try to run an ios example. Below is the log I'm getting while running the ios example app.</p>
  <p>Can anyone help me with this?</p>
  <pre><code>Running pod install...
  CocoaPods' output:
      Analyzing dependencies
  
      Inspecting targets to integrate
        Using `ARCHS` setting to build architectures of target `Pods-Runner`: (``)
  
      Fetching external sources
      -&gt; Fetching podspec for `Flutter` from `.symlinks/flutter/ios`
      -&gt; Fetching podspec for `flutter_plugin` from `.symlinks/plugins/flutter_plugin/ios`
  
      Resolving dependencies of `Podfile`
  
      Comparing resolved specification to the sandbox manifest
        A Flutter
        A flutter_plugin
  
      Downloading dependencies
  
      -&gt; Installing Flutter (1.0.0)
  
      -&gt; Installing flutter_plugin (0.0.1)
        - Running pre-install hooks
      [!] Unable to determine Swift version for the following pods:
  
      - `flutter_plugin` does not specify a Swift version and none of the targets (`Runner`) integrating it has the `SWIFT_VERSION` attribute set. Please contact the author or set the `SWIFT_VERSION` attribute in at least one of the targets that integrate this pod.
  
      /Library/Ruby/Gems/2.3.0/gems/cocoapods-1.6.1/lib/cocoapods/installer/xcode/target_validator.rb:115:in `verify_swift_pods_swift_version'
      /Library/Ruby/Gems/2.3.0/gems/cocoapods-1.6.1/lib/cocoapods/installer/xcode/target_validator.rb:37:in `validate!'
      /Library/Ruby/Gems/2.3.0/gems/cocoapods-1.6.1/lib/cocoapods/installer.rb:459:in `validate_targets'
      /Library/Ruby/Gems/2.3.0/gems/cocoapods-1.6.1/lib/cocoapods/installer.rb:138:in `install!'
      /Library/Ruby/Gems/2.3.0/gems/cocoapods-1.6.1/lib/cocoapods/command/install.rb:48:in `run'
      /Library/Ruby/Gems/2.3.0/gems/claide-1.0.2/lib/claide/command.rb:334:in `run'
      /Library/Ruby/Gems/2.3.0/gems/cocoapods-1.6.1/lib/cocoapods/command.rb:52:in `run'
      /Library/Ruby/Gems/2.3.0/gems/cocoapods-1.6.1/bin/pod:55:in `&lt;top (required)&gt;'
      /usr/local/bin/pod:22:in `load'
      /usr/local/bin/pod:22:in `&lt;main&gt;'
  
  Error output from CocoaPods:
          [33mWARNING: CocoaPods requires your terminal to be using UTF-8 encoding.
          Consider adding the following to ~/.profile:
  Error running pod install
  </code></pre>