Fix "Python" casing in a few places (GH-9001)

diff --git a/Doc/library/idle.rst b/Doc/library/idle.rst
index 58e6193..0eb1b44 100644
--- a/Doc/library/idle.rst
+++ b/Doc/library/idle.rst
@@ -303,7 +303,7 @@
    and open docs.python.org showing the latest Python documentation.
 
 Turtle Demo
-   Run the turtledemo module with example python code and turtle drawings.
+   Run the turtledemo module with example Python code and turtle drawings.
 
 Additional help sources may be added here with the Configure IDLE dialog under
 the General tab.