Update version to 0.1.21

Author: ataffanel

setup.py

@@ -9,7 +9,7 @@
 
 setup(
     name='cflib',
-    version='0.1.20.1',
+    version='0.1.21',
     packages=find_packages(exclude=['examples', 'test']),
 
     description='Crazyflie python driver',