Updated _Sidebar (markdown)

_Sidebar.md

@@ -2,7 +2,7 @@
 - [[Installation|Getting Started]]
 - [[Learn Micropython|Learn Micropython]]
 - [[Differences to CPython|Differences]]
-- [micropython-lib](https://github.com/micropython/micropython-lib): ported core libraries
+- [micropython-lib](https://github.com/micropython/micropython-lib): ported stdlib
 
 ## Python Boards and MCUs
 - [The pyb module](http://docs.micropython.org/en/latest/library/pyb.html)