title: Elm `update` is not executing the case statement when dropdown's value is changed
body: <p>I am new to Elm. I am not able to call the update function once the dropdown value changes.</p>
  
  <p>Scenario:
  I have two dropdowns <code>Grade</code> and <code>Environment</code>. What I want is when <code>Grade</code> dropdown values change, the options of <code>Environment</code> dropdown will dependently change.</p>
  
  <p>For example, if <code>Grade</code> dropdown value is <code>3</code> then the options of <code>Environment</code> should change to <code>Imagine Math</code></p>
  
  <pre><code>    gradeDropdown : String -&gt; List String -&gt; Html Msg
      gradeDropdown grade grades =
          let
              buildOption =
                  gradeOption grade
          in
              select [ class "importWizard--gradeSelection", name "gradeSelection", onChange (UpdateStudent Grade) ]
                  (map buildOption grades)
  
      gradeOption : String -&gt; String -&gt; Html Msg
      gradeOption optSelectedVal temp =
          let
              optSelected =
                  temp == optSelectedVal
          in
              option [ value temp, selected optSelected ] [ text temp ]
  
      environmentDropdown : Model -&gt; String -&gt; List String -&gt; String -&gt; Html Msg
      environmentDropdown model learningEnvironment learningEnvironments selectedGrade =
          let
              buildOption =
                  environmentOption model learningEnvironment
              blueprint_grades = ["PreKindergarten", "Kindergarten", "1"]
              environmentDropdownOption =
                if (selectedGrade == "" || (List.member selectedGrade blueprint_grades)) then
                  ["Blueprint"]
                else if (selectedGrade == "2") then
                  learningEnvironments
                else
                  ["Imagine Math"]
          in
              select [
                class "importWizard--learningEnvironmentSelection"
                , name "learningEnvironmentSelection"
                , onChange (UpdateStudent LearningEnvironments)
              ]
              (map buildOption environmentDropdownOption)
  
      environmentOption : Model -&gt; String -&gt; String -&gt; Html Msg
      environmentOption model optSelectedVal temp =
          let
              optSelected =
                  temp == optSelectedVal
          in
              option [ value temp, selected optSelected ] [ text temp ]
  </code></pre>
  
  <p>And in <strong>Update</strong></p>
  
  <pre><code>update : Flags -&gt; Msg -&gt; Model -&gt; ( Model, Cmd Msg )
      update flags message model =
          case message of
              UpdateStudent updateType newValue -&gt;
                  let
                      validate =
                          validateStudent flags validatableFieldsForScreen
                  in
                      case updateType of
                          LastName -&gt;
                              ( validate { model | lastName = newValue } &lt;| Just LastNameField, Cmd.none )
  
                          FirstName -&gt;
                              ( validate { model | firstName = newValue } &lt;| Just FirstNameField, Cmd.none )
  
                          Sin -&gt;
                              ( validate { model | sin = newValue } &lt;| Just SinField, Cmd.none )
  
                          Grade -&gt;
                              ( validate { model | grade = newValue, selectedGrade = newValue } Nothing, Cmd.none )
  
                          LearningEnvironments -&gt;
                              ( validate { model | learningEnvironments = newValue } Nothing, Cmd.none )
  </code></pre>
  
  <p><strong>View:</strong></p>
  
  <pre><code>, td [ class wizardTableInput ] [ gradeDropdown model.grade flags.grades ]
  , td [ class wizardTableInput ] [ environmentDropdown model model.learningEnvironments flags.learningEnvironments model.selectedGrade ]
  </code></pre>
  
  <p>In this code, the environment dropdown's value is changing, however the model's value is not updated. From what I understand, I can see is environment dropdown's id re-rendered, but it is not updating the model's value of <code>learningEnvironments</code>. This means it is not executing the <code>update</code> function matching <code>LearningEnvironments</code>.</p>