Fix EMCAScript → ECMAScript typos (#417)

Author: mathiasbynens

index.bs

@@ -1101,7 +1101,7 @@ explicitly test that scripts running in sandboxes work in all implementations.
 
 ## Sandbox Realms ## {#sandbox-realm}
 
-Each sandbox is a unique EMCAScript [=Realm=]. However the sandbox realm
+Each sandbox is a unique ECMAScript [=Realm=]. However the sandbox realm
 provides access to platform objects in an existing {{Window}} realm via
 {{SandboxProxy}} objects.
 
@@ -4263,7 +4263,7 @@ script.Handle = text;
 The <code>script.Handle</code> type represents a handle to an object owned by
 the ECMAScript runtime. The handle is only valid in a specific [=Realm=].
 
-Each EMCAScript [=Realm=] has a corresponding <dfn>handle object map</dfn>. This is a
+Each ECMAScript [=Realm=] has a corresponding <dfn>handle object map</dfn>. This is a
 strong [=/map=] from handle ids to their corresponding objects.
 
 #### The script.LocalValue Type #### {#type-script-LocalValue}