Use proper syntax for gem install

Author: evil159

.circleci/config.yml

@@ -104,7 +104,7 @@ jobs:
             # allegedly, this issue is resolved in https://github.com/CocoaPods/CocoaPods/pull/12082,
             # pinning can be removed after the above fix is released
             gem uninstall activesupport --version '>= 7.0.8' --ignore-dependencies
-            gem install activesupport '7.0.8'
+            gem install activesupport --version '7.0.8'
       - flutter/install_sdk_and_pub:
           version: 3.13.6
           app-dir: example