simpleFilter dropdown button now works works angular-bootstrap

this change, the addition of the dropdown attribute to the encapsulating div and dropdown-toggle attribute on the dropdown button does not modify any original behavior, but does allow the button to work with the angular-bootstrap

Author: AllenBW

src/filters/simple-filter.html

@@ -2,8 +2,8 @@
   <form>
     <div class="form-group">
       <div class="input-group">
-        <div class="input-group-btn">
-          <button type="button" class="btn btn-default dropdown-toggle filter-fields" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
+        <div dropdown class="input-group-btn">
+          <button dropdown-toggle type="button" class="btn btn-default dropdown-toggle filter-fields" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
             {{currentField.title}}
             <span class="caret"></span>
           </button>