Update pytz from 2019.2 to 2019.3

requirements/docs.txt

@@ -59,9 +59,9 @@ MarkupSafe==1.1.1 \
     --hash=sha256:cd5df75523866410809ca100dc9681e301e3c27567cf498077e8551b6d20e42f \
     --hash=sha256:e249096428b3ae81b08327a63a485ad0878de3fb939049038579ac0ef61e17e7
 # pytz is required by Babel, celery
-pytz==2019.2 \
-    --hash=sha256:26c0b32e437e54a18161324a2fca3c4b9846b74a8dccddd843113109e1116b32 \
-    --hash=sha256:c894d57500a4cd2d5c71114aaab77dbab5eabd9022308ce5ac9bb93a60a6f0c7
+pytz==2019.3 \
+    --hash=sha256:1c557d7d0e871de1f5ccd5833f60fb2550652da6be2693c1e02300743d21500d \
+    --hash=sha256:b02c06db6cf09c12dd25137e563b31700d3b80fcc4ad23abb7a315f2789819be
 # requests is required by Sphinx
 requests==2.22.0 \
     --hash=sha256:11e007a8a2aa0323f5a921e9e6a2d7e4e67d9877e85773fba9ba6419025cbeb4 \