API Doc link: make releases/RC's point to their own version of the doc.

Sounds kind of stupid to have 2.79 pointing to "current" which is now
2.80 API doc... Let's try to avoid that in future.

release/scripts/startup/bl_operators/wm.py

@@ -1023,7 +1023,8 @@ class WM_OT_doc_view(Operator):
 
     doc_id: doc_id
     if bpy.app.version_cycle in {"release", "rc"}:
-        _prefix = ("https://docs.blender.org/api/current")
+        _prefix = ("https://docs.blender.org/api/%d.%d%s" %
+                   (bpy.app.version[0], bpy.app.version[1], bpy.app.version_char))
     else:
         _prefix = ("https://docs.blender.org/api/master")