🔒 Bump twisted version to 20.3.0 (#2135)

Because of a detected vulnerability with prior versions of twisted:

**See also**: GHSA-h96w-mmrf-2h6v

Author: opacam

pythonforandroid/recipes/twisted/__init__.py

@@ -2,7 +2,7 @@
 
 
 class TwistedRecipe(CythonRecipe):
-    version = '19.7.0'
+    version = '20.3.0'
     url = 'https://github.com/twisted/twisted/archive/twisted-{version}.tar.gz'
 
     depends = ['setuptools', 'zope_interface', 'incremental', 'constantly']