Update certifi from 2018.4.16 to 2018.8.13 (#3912)

requirements/common.txt

@@ -209,9 +209,9 @@ urllib3==1.22 \
     --hash=sha256:06330f386d6e4b195fbfc736b297f58c5a892e4440e54d294d7004e3a9bbea1b \
     --hash=sha256:cc44da8e1145637334317feebd728bd869a35285b93cbb4cca2577da7e62db4f
 
-certifi==2018.4.16 \
-    --hash=sha256:9fa520c1bacfb634fa7af20a76bcbd3d5fb390481724c597da32c719a7dca4b0 \
-    --hash=sha256:13e698f54293db9f89122b0581843a782ad0934a4fe0172d2a980ba77fc61bb7
+certifi==2018.8.13 \
+    --hash=sha256:b6e8b28b2b7e771a41ecdd12d4d43262ecab52adebbafa42c77d6b57fb6ad3a4 \
+    --hash=sha256:4c1d68a1408dd090d2f3a869aa94c3947cc1d967821d1ed303208c9f41f0f2f4
 
 # required by requests
 chardet==3.0.4 \