Update certifi from 2019.3.9 to 2019.6.16 (#315)

Author: pyup-bot

docker/build_scripts/py36-requirements.txt

@@ -1,8 +1,8 @@
 # pip requirements for cpython 3.6
 # NOTE: certifi has GPG signatures; could download and verify independently.
-certifi==2019.3.9 \
-    --hash=sha256:59b7658e26ca9c7339e00f8f4636cdfe59d34fa37b9b04f6f9e9926b3cece1a5 \
-    --hash=sha256:b26104d6835d1f5e49452a26eb2ff87fe7090b89dfcaee5ea2212697e1e1d7ae
+certifi==2019.6.16 \
+    --hash=sha256:046832c04d4e752f37383b628bc601a7ea7211496b4638f6514d0e5b9acc4939 \
+    --hash=sha256:945e3ba63a0b9f577b1395204e13c3a231f9bc0223888be653286534e5873695
 auditwheel==2.0.0 \
     --hash=sha256:63fe2fdda4d6c5f7b04e3982896428e3c243fdf8b8543aaa567bf0e1ce26b44a \
     --hash=sha256:5328dc30953dd51b6c8f18bb0073a0d9c7e2a1cbccfc913a0998125d1fc3f29d