Point API doc back to master one.

Now that 2.8 is master again...
Still have to update 2.7 thingy there, now (and update API doc site
 accordingly, too).

release/scripts/startup/bl_operators/wm.py

@@ -1026,7 +1026,7 @@ class WM_OT_doc_view(Operator):
     if bpy.app.version_cycle == "release":
         _prefix = ("https://docs.blender.org/api/current")
     else:
-        _prefix = ("https://docs.blender.org/api/blender2.8")
+        _prefix = ("https://docs.blender.org/api/master")
 
     def execute(self, context):
         url = _wm_doc_get_id(self.doc_id, do_url=True, url_prefix=self._prefix)