[typed-om] Whoops, all these clauses are for when is2D is *false*. Fixes w3c#738.

Author: tabatkins

css-typed-om/Overview.bs

@@ -5296,7 +5296,7 @@ length3.toString(); // "42px";
 
     1. Let |s| initially be the empty [=string=].
 
-    2. If |this|’s {{CSSTransformValue/is2D}} internal slot is `true`:
+    2. If |this|’s {{CSSTransformValue/is2D}} internal slot is `false`:
         1. Append "translate3d(" to |s|.
 
         2. Serialize |this|’s {{CSSTranslate/x}} internal slot,
@@ -5335,7 +5335,7 @@ length3.toString(); // "42px";
 
     1. Let |s| initially be the empty [=string=].
 
-    2. If |this|’s {{CSSTransformValue/is2D}} internal slot is `true`:
+    2. If |this|’s {{CSSTransformValue/is2D}} internal slot is `false`:
         1. Append "rotate3d(" to |s|.
 
         2. Serialize |this|’s {{CSSRotate/x}} internal slot,
@@ -5374,7 +5374,7 @@ length3.toString(); // "42px";
 
     1. Let |s| initially be the empty [=string=].
 
-    2. If |this|’s {{CSSTransformValue/is2D}} internal slot is `true`:
+    2. If |this|’s {{CSSTransformValue/is2D}} internal slot is `false`:
         1. Append "scale3d(" to |s|.
 
         2. Serialize |this|’s {{CSSScale/x}} internal slot,