Fix table formatting in scanning.bs

Author: reillyeon

scanning.bs

@@ -289,7 +289,7 @@ spec:web-bluetooth
         Let |scan| be a [=new=] {{BluetoothLEScan}} instance
         whose fields are initialized as in the following table:
         <table class="data">
-          <thead><th>Field</th><th>Initial value</th></thead>
+          <thead><tr><th>Field</th><th>Initial value</th></tr></thead>
           <tr><td>{{BluetoothLEScan/filters}}</td><td>|filters|</td></tr>
           <tr>
             <td>{{BluetoothLEScan/keepRepeatedDevices}}</td>
@@ -803,9 +803,11 @@ the [=current settings object=]'s [=relevant global object=] is no longer
   </p>
   <table class="data" dfn-for="Bluetooth" dfn-type="attribute">
     <thead>
-      <th>Internal Slot</th>
-      <th>Initial Value</th>
-      <th>Description (non-normative)</th>
+      <tr>
+        <th>Internal Slot</th>
+        <th>Initial Value</th>
+        <th>Description (non-normative)</th>
+      </tr>
     </thead>
     <tr>
       <td><dfn>\[[activeScans]]</dfn></td>
@@ -823,9 +825,11 @@ the [=current settings object=]'s [=relevant global object=] is no longer
   </p>
   <table class="data" dfn-for="BluetoothDevice" dfn-type="attribute">
     <thead>
-      <th>Internal Slot</th>
-      <th>Initial Value</th>
-      <th>Description (non-normative)</th>
+      <tr>
+        <th>Internal Slot</th>
+        <th>Initial Value</th>
+        <th>Description (non-normative)</th>
+      </tr>
     </thead>
     <tr>
       <td><dfn>\[[returnedFromScans]]</dfn></td>