title: admin-create-user command doesn't work properly
body: <p>I'm trying to run admin-create-user cli command as shown in the official doc, but it doesn't seems to run properly.</p>
  
  <p>I don't get all attributes created event though they were in the command. I always get only the last attribute typed in the command. </p>
  
  <p>am I doing something wrong? is there any solution?</p>
  
  <pre class="lang-sh prettyprint-override"><code>aws cognito-idp admin-create-user --user-pool-id us-west-2_aaaaaaaaa --username diego@example.com --user-attributes=Name=email,Value=kermit2@somewhere.com,Name=phone_number,Value="+15555551212" --message-action SUPPRESS
  
  </code></pre>
  
  <p>and I'm getting</p>
  
  <pre><code>{
      "User": {
          "Username": "diego@example.com",
          "Enabled": true,
          "UserStatus": "FORCE_CHANGE_PASSWORD",
          "UserCreateDate": 1566470568.864,
          "UserLastModifiedDate": 1566470568.864,
          "Attributes": [
              {
                  "Name": "sub",
                  "Value": "5dac8ce5-2997-4185-b862-86cf15aede77"
              },
              {
                  "Name": "phone_number",
                  "Value": "+15555551212"
              }
          ]
      }
  }
  </code></pre>
  
  <p>instead of</p>
  
  <pre><code>{
    "User": {
        "Username": "7325c1de-b05b-4f84-b321-9adc6e61f4a2",
        "Enabled": true,
        "UserStatus": "FORCE_CHANGE_PASSWORD",
        "UserCreateDate": 1548099495.428,
        "UserLastModifiedDate": 1548099495.428,
        "Attributes": [
            {
                "Name": "sub",
                "Value": "7325c1de-b05b-4f84-b321-9adc6e61f4a2"
            },
            {
                "Name": "phone_number",
                "Value": "+15555551212"
            },
            {
                "Name": "email",
                "Value": "diego@example.com"
            }
        ]
    }
  }
  </code></pre>