update changelog

Author: timfel

CHANGELOG.md

@@ -5,6 +5,7 @@ language runtime. The main focus is on user-observable behavior of the engine.
 
 ## Version 19.3.0
 
+* Implement `gc.{enable,disable,isenabled}` as stubs
 * Implement `charmap_build` function
 * Implement `hexversion` in sys module
 * Implement `_lzma` module
@@ -13,6 +14,7 @@ language runtime. The main focus is on user-observable behavior of the engine.
 * Fix destructuring assignments of arbitrary iterators
 * Fix `dict.__contains__` for dictionaries with only `str` keys for subclasses of `str`
 * Support NumPy 1.16.4 and Pandas 0.25.0
+* Support `timeit` module
 * Support importing Java classes using normal Python import syntax when the package is known
 * Improve performance across many Python benchmarks