Fix markup error

Two tables were missing `<tr>` in their head.

Author: tabatkins

index.bs

@@ -8538,7 +8538,7 @@ JavaScript Object values.
     constrained among the three string types.
     The following conversions have the described results:
     <table class="data">
-        <thead><th>Value</th><th>Passed to type</th><th>Result</th></thead>
+        <thead><tr><th>Value</th><th>Passed to type</th><th>Result</th></thead>
         <tr>
             <td><code>{"😞": 1}</code></td>
             <td><code>[=record=]&lt;ByteString, double></code></td>
@@ -12579,9 +12579,10 @@ the table, and the operation must have the return type given in the third column
 
 <table id="table-default-method-steps" class="data">
 <thead>
-    <th>[=Identifier=]
-    <th>[=Default method steps=]
-    <th>[=Return type=]</th>
+    <tr>
+        <th>[=Identifier=]
+        <th>[=Default method steps=]
+        <th>[=Return type=]</th>
 <tbody>
     <tr>
         <td>"<code>toJSON</code>"