spacebars: Allow partial optimisation within table's

This prevents optimisation of <table> and <tr> elements,
but allows all children of those elements to be optimised.

packages/spacebars-compiler/optimizer.js

@@ -55,7 +55,9 @@ CanOptimizeVisitor.def({
       // browser will insert a TBODY.  If we just `createElement("table")` and
       // `createElement("tr")`, on the other hand, no TBODY is necessary
       // (assuming IE 8+).
-      return OPTIMIZABLE.NONE;
+      return OPTIMIZABLE.PARTS;
+    } else if (tagName === 'tr'){
+      return OPTIMIZABLE.PARTS;
     }
 
     var children = tag.children;