fix the complexity comments for attribute APIs

sky/specs/apis.md

 APIs
 ====
 
 The Sky core API
 ----------------
 
 ```javascript
 module 'sky:core' {
 
   // EVENTS
@@ skipping 72 matching lines @@
 
   class Attr {
     constructor (String name, String value = ''); // O(1)
     readonly attribute String name; // O(1)
     readonly attribute String value; // O(1)
   }
 
   abstract class Element : ParentNode {
     readonly attribute String tagName; // O(1)
 
-    Boolean hasAttribute(String name); // O(N) in arguments
-    String getAttribute(String name); // O(N) in arguments
-    void setAttribute(String name, String value = ''); // O(N) in arguments
-    void removeAttribute(String name); // O(N) in arguments
+    Boolean hasAttribute(String name); // O(N) in number of attributes
+    String getAttribute(String name); // O(N) in number of attributes
+    void setAttribute(String name, String value = ''); // O(N) in number of attributes
+    void removeAttribute(String name); // O(N) in number of attributes
     
     // Returns a new Array and new Attr instances every time.
-    Array<Attr> getAttributes(); // O(N) in arguments
+    Array<Attr> getAttributes(); // O(N) in number of attributes
 
     readonly attribute ShadowRoot? shadowRoot; // O(1) // returns the shadow root
     Array<ContentElement> getDestinationInsertionPoints(); // O(N) in number of insertion points the node is in
 
     virtual void attributeChangeCallback(String name, String? oldValue, String? newValue); // noop
     // TODO(ianh): does a node ever need to know when it's been redistributed?
   }
 
   class Text : Node {
     constructor (String value = ''); // O(1)
@@ skipping 316 matching lines @@
   the core mojo fabric JS API   sky:mojo:fabric:core
   the asyncWait/cancelWait mojo fabric JS API (interface to IPC thread)  sky:mojo:fabric:ipc
   the mojom for the shell, proxying through C++ so that the shell pipe isn't exposed  sky:mojo:shell
   the sky API  sky:core
   the sky debug symbols for private APIs  sky:debug
 ```
 
 TODO(ianh): determine if we want to separate the "this" from the
 Document, especially for Modules, so that exposing a module's element
 doesn't expose the module's exports attribute.