Fix typos: substraction -> subtraction, suppported -> supported

Author: delirious-lettuce

prompt_toolkit/reactive.py

@@ -16,7 +16,7 @@
  of a filter happens by calling it.
 
 - Integer: for binding integer values. Reactive operations (like addition and
- substraction) are not suppported. Resolving the actual value happens by
+ subtraction) are not supported. Resolving the actual value happens by
  casting it to int, like ``int(integer)``. This way, it is possible to use
  normal integers as well for static values.
 """