Hold back urllib 1.2.4 upgrade

Author: mythmon

requirements/constraints.txt

@@ -7,6 +7,7 @@ attrs==18.2.0 \
 botocore==1.12.28 \
     --hash=sha256:b7868bcfddecd269e8f60e9c9b0079e2fa74bd21e0dae89fce70c012127ea4a0 \
     --hash=sha256:e28316bcda7af32dc7273a3842678c38b2c5f80c48f5e9443d7fdd35b138ea9a
+    # NB: botocore 1.12.28 is holding urllib3 at < 1.24. When botocore supports urllib 1.24, remove the pyup hold.
 certifi==2018.10.15 \
     --hash=sha256:339dc09518b07e2fa7eda5450740925974815557727d6bd35d319c1524a04a4c \
     --hash=sha256:6d58c986d22b038c8c0df30d639f23a3e6d172a05c3583e766f4c0b785c0986a
@@ -143,9 +144,10 @@ uritemplate==3.0.0 \
     --hash=sha256:01c69f4fe8ed503b2951bef85d996a9d22434d2431584b5b107b2981ff416fbd \
     --hash=sha256:1b9c467a940ce9fb9f50df819e8ddd14696f89b9a8cc87ac77952ba416e0a8fd \
     --hash=sha256:c02643cebe23fc8adb5e6becffe201185bf06c40bda5c0b4028a93f1527d011d
-urllib3==1.24 \
-    --hash=sha256:8819bba37a02d143296a4d032373c4dd4aca11f6d4c9973335ca75f9c8475f59 \
-    --hash=sha256:41c3db2fc01e5b907288010dec72f9d0a74e37d6994e6eb56849f59fea2265ae
+urllib3==1.23 \
+    --hash=sha256:b5725a0bd4ba422ab0e66e89e030c806576753ea3ee08554382c14e685d117b5 \
+    --hash=sha256:a68ac5e15e76e7e5dd2b8f94007233e01effe3e50e8daddf69acfd81cb686baf
+    # pyup: <1.24 # botocore 1.12.28 has requirement urllib3<1.24,>=1.20
 webencodings==0.5.1 \
     --hash=sha256:a0af1213f3c2226497a97e2b3aa01a7e4bee4f403f95be16fc9acd2947514a78 \
     --hash=sha256:b36a1c245f2d304965eb4e0a82848379241dc04b865afcc4aab16748587e1923