Update idna from 2.7 to 2.8 (#4344)

requirements/common.txt

@@ -236,9 +236,9 @@ certifi==2018.11.29 \
 chardet==3.0.4 \
     --hash=sha256:fc323ffcaeaed0e0a02bf4d117757b98aed530d9ed4531e3e15460124c106691 \
     --hash=sha256:84ab92ed1c4d4f16916e05906b6b75a6c0fb5db821cc65e70cbd64a3e2a5eaae
-idna==2.7 \
+idna==2.8 \
-    --hash=sha256:156a6814fb5ac1fc6850fb002e0852d56c0c8d2531923a51032d1b70760e186e \
+    --hash=sha256:ea8b7f6188e6fa117537c3df7da9fc686d485087abf6ac197f9c46432f7e4a3c \
-    --hash=sha256:684a38a6f903c1d71d6d5fac066b58d7768af4de2b832e426ec79c30daa94a16
+    --hash=sha256:c357b3f628cf53ae2c4c05627ecc484553142ca23264e593d327bcde5e9c3407
 
 # required for taskcluster
 slugid==1.0.7 --hash=sha256:6dab3c7eef0bb423fb54cb7752e0f466ddd0ee495b78b763be60e8a27f69e779