title: Why flutter `pub get` change pubspec.lock?
body: <p>When I execute <code>flutter pub get</code> or <code>pub get</code>, these changes their <code>pubspec.lock</code> sometimes like below.</p>
  <pre><code>sdks:
  -  dart: &quot;&gt;=2.10.2 &lt;=2.11.0-213.1.beta&quot;
  +  dart: &quot;&gt;=2.10.2 &lt;2.11.0&quot;
  </code></pre>
  <p>I thought <code>pub get</code> is nealy equal to CocoaPods command <code>pod install</code> which does not modify lock file.<br>
  Why <code>pub get</code> update lock file?</p>