Change margins to margin (#370)

Author: jgraham

index.bs

@@ -3498,7 +3498,7 @@ The [=remote end steps=] with <var ignore>session</var> and |command parameters|
    |context| for any reason then return [=error=] with [=error code=]
    [=unsupported operation=].
 
-1. Let |margins| be the value of the <code>margins</code> field of |command
+1. Let |margin| be the value of the <code>margin</code> field of |command
    parameters| if present, or otherwise a [=/map=] matching the
    <code>browsingContext.PrintMarginParameters</code> with the fields set to
    their default values.
@@ -3539,16 +3539,16 @@ The [=remote end steps=] with <var ignore>session</var> and |command parameters|
              "<code>portrait</code>" otherwise |page size|["<code>width</code>"]
        <tr>
          <td>Top margin, in cm
-         <td>|margins|["<code>top</code>"]
+         <td>|margin|["<code>top</code>"]
        <tr>
          <td>Bottom margin, in cm
-         <td>|margins|["<code>bottom</code>"]
+         <td>|margin|["<code>bottom</code>"]
        <tr>
          <td>Left margin, in cm
-         <td>|margins|["<code>left</code>"]
+         <td>|margin|["<code>left</code>"]
        <tr>
          <td>Right margin, in cm
-         <td>|margins|["<code>right</code>"]
+         <td>|margin|["<code>right</code>"]
      </table>
 
      In addition, the following formatting hints should be applied by the UA: