title: Error running Serverless Framework command after upgrading to v3
body: <p>I recently upgraded my Serverless Framework project from <code>v2.7</code> to <code>v3.0.1</code>. After doing so, any time I run <code>serverless deploy</code> I get the following error:</p>
  <pre><code>Environment: win32, node 14.18.1, framework 3.0.1, plugin 6.0.0, SDK 4.3.0
  Docs:        docs.serverless.com
  Support:     forum.serverless.com
  Bugs:        github.com/serverless/serverless/issues
  
  Error:
  TypeError: validate is not a function
      at ConfigSchemaHandler.validateConfig (C:\Users\MainPC\AppData\Roaming\nvm\v14.18.1\node_modules\serverless\lib\classes\config-schema-handler\index.js:101:5)
      at async Service.validate (C:\Users\MainPC\AppData\Roaming\nvm\v14.18.1\node_modules\serverless\lib\classes\service.js:267:5)
      at async Serverless.run (C:\Users\MainPC\AppData\Roaming\nvm\v14.18.1\node_modules\serverless\lib\serverless.js:162:28)
      at async C:\Users\MainPC\AppData\Roaming\nvm\v14.18.1\node_modules\serverless\scripts\serverless.js:675:9
  </code></pre>
  <p>I have tried the following:</p>
  <ul>
  <li>Creating a new &quot;hello world&quot; project by running <code>serverless</code> and selecting the NodeJS starter project</li>
  <li>Uninstalling <code>nvm</code> and re-installing NodeJS v14.18.1 completely</li>
  <li>Deleted every globally installed NPM module and re-installed <em>only</em> SLS from scratch</li>
  </ul>
  <p>I am now running standalone v14 Node without NVM (on Windows 10) and still the error persists. Reverting to v2.7 resolves the error.</p>
  <p>Nobody else seems to be suffering this issue. Can anyone offer some assistance?</p>
  <hr />
  <p>For those asking for the template, the error even happens on this demo template that Serverless itself generates for a new project:</p>
  <pre><code>service: testing-v3
  
  frameworkVersion: '3'
  
  provider:
    name: aws
    runtime: nodejs14.x
  
  functions:
    hello:
      handler: handler.hello
  </code></pre>
  <p>I am pretty confident the issue is either an installation issue or something specific to v3, or both.</p>