replace RequireObjectCoercible with Object check (#290)

spec.html

@@ -119,15 +119,16 @@ <h1>
     <dl class="header">
     </dl>
     <emu-alg>
-      1. Let _O_ be ? RequireObjectCoercible(_this_).
-      1. If _O_ is _home_, then
+      1. If _this_ is not an Object, then
+        1. Throw a *TypeError* exception.
+      1. If _this_ is _home_, then
         1. NOTE: Throwing here emulates assignment to a non-writable data property on the _home_ object in strict mode code.
         1. Throw a *TypeError* exception.
-      1. Let _desc_ be ? _O_.[[GetOwnProperty]](_p_).
+      1. Let _desc_ be ? _this_.[[GetOwnProperty]](_p_).
       1. If _desc_ is *undefined*, then
-        1. Perform ? CreateDataPropertyOrThrow(_O_, _p_, _v_).
+        1. Perform ? CreateDataPropertyOrThrow(_this_, _p_, _v_).
       1. Else,
-        1. Perform ? Set(_O_, _p_, _v_, *true*).
+        1. Perform ? Set(_this_, _p_, _v_, *true*).
       1. Return ~unused~.
     </emu-alg>
   </emu-clause>