Update cryptography to 2.4.2 (#1356)

This PR updates [cryptography](https://pypi.org/project/cryptography) from **2.4.1** to **2.4.2**.



*The bot wasn't able to find a changelog for this release. [Got an idea?](https://github.com/pyupio/changelogs/issues/new)*

<details>
  <summary>Links</summary>
  
  - PyPI: https://pypi.org/project/cryptography
  - Changelog: https://pyup.io/changelogs/cryptography/
  - Repo: https://github.com/pyca/cryptography
</details>

requirements.txt

@@ -83,26 +83,26 @@ configparser==3.5.0 \
 django-configurations==2.1 \
     --hash=sha256:71d9acdff33aa034f0157b0b3d23629fe0cd499bf4d0b6d699b9ca0701d952e8 \
     --hash=sha256:e70433eeed10549d30bf5ca386c962505ff9f492893dd2483c52af536347adce
-cryptography==2.4.1 \
-    --hash=sha256:02915ee546b42ce513e8167140e9937fc4c81a06a82216e086ccce51f347948a \
-    --hash=sha256:03cc8bc5a69ae3d44acf1a03facdb7c10a94c67907862c563e10efe72b737977 \
-    --hash=sha256:07f76bde6815c55195f3b3812d35769cc7c765144c0bb71ae45e02535d078591 \
-    --hash=sha256:13eac1c477b9af7e9a9024369468d08aead6ad78ed599d163ad046684474364b \
-    --hash=sha256:179bfb585c5efc87ae0e665770e4896727b92dbc1f810c761b1ebf8363e2fec8 \
-    --hash=sha256:414af0ba308e74c1f8bc5b11befc86cb66b10be8959547786f64258830d2096f \
-    --hash=sha256:41a1ca14f255df8c44dd22c6006441d631d1589104045ec7263cc47e9772f41a \
-    --hash=sha256:54947eb98bc4eef99ddf49f45d2694ea5a3929ab3edc9806ad01967368594d82 \
-    --hash=sha256:5bac7a2abda07d0c3c8429210349bb54149ad8940dc7bcffedcd56519b410a3c \
-    --hash=sha256:7f41af8c586bed9f59cfe8832d818b3b75c860d7025da9cd2db76875a72ff785 \
-    --hash=sha256:8004fae1b3cb2dbd90a011ad972e49a7e78a871b89c70cc7213cf4ebd2532bcb \
-    --hash=sha256:8e0eccadc3b465e12c50a5b8fb4d39cf401b44d7bb9936c70fddb5e5aaf740d5 \
-    --hash=sha256:95b4741722269cfdc134fec23b7ae6503ee2aea83d0924cfee6d6ec54cd42d8e \
-    --hash=sha256:a06f5aa6d7a94531dfe82eb2972e669258c452fe9cf88f76116610de4c789785 \
-    --hash=sha256:b0833d27c7eb536bc27323a1e8e22cb39ebac78c4ef3be0167ba40f447344808 \
-    --hash=sha256:b72dec675bc59a01edc96616cd48ec465b714481caa0938c8bbca5d18f17d5df \
-    --hash=sha256:c800ddc23b5206ce025f23225fdde89cdc0e64016ad914d5be32d1f602ce9495 \
-    --hash=sha256:c980c8c313a5e014ae12e2245e89e7b30427e5a98cbb88afe478ecae85f3abaa \
-    --hash=sha256:e85b410885addaeb31a867eabcefc9ef4a7e904ad45eac9e60a763a54b244626
+cryptography==2.4.2 \
+    --hash=sha256:0ff4a3d6ea86aa0c9e06e92a9f986de7ee8231f36c4da1b31c61a7e692ef3378 \
+    --hash=sha256:63b064a074f8dc61be81449796e2c3f4e308b6eba04a241a5c9f2d05e882c681 \
+    --hash=sha256:b4fc04326b2d259ddd59ed8ea20405d2e695486ab4c5e1e49b025c484845206e \
+    --hash=sha256:0eb83a24c650a36f68e31a6d0a70f7ad9c358fa2506dc7b683398b92e354a038 \
+    --hash=sha256:af12dfc9874ac27ebe57fc28c8df0e8afa11f2a1025566476b0d50cdb8884f70 \
+    --hash=sha256:5ecaf9e7db3ca582c6de6229525d35db8a4e59dc3e8a40a331674ed90e658cbf \
+    --hash=sha256:3cdc5f7ca057b2214ce4569e01b0f368b3de9d8ee01887557755ccd1c15d9427 \
+    --hash=sha256:21e63dd20f5e5455e8b34179ac43d95b3fb1ffa54d071fd2ed5d67da82cfe6dc \
+    --hash=sha256:8908f1db90be48b060888e9c96a0dee9d842765ce9594ff6a23da61086116bb6 \
+    --hash=sha256:70596e90398574b77929cd87e1ac6e43edd0e29ba01e1365fed9c26bde295aa5 \
+    --hash=sha256:471a097076a7c4ab85561d7fa9a1239bd2ae1f9fd0047520f13d8b340bf3210b \
+    --hash=sha256:70c2b04e905d3f72e2ba12c58a590817128dfca08949173faa19a42c824efa0b \
+    --hash=sha256:6afe324dfe6074822ccd56d80420df750e19ac30a4e56c925746c735cf22ae8b \
+    --hash=sha256:da5b5dda4aa0d5e2b758cc8dfc67f8d4212e88ea9caad5f61ba132f948bab859 \
+    --hash=sha256:1699f3e916981df32afdd014fb3164db28cdb61c757029f502cb0a8c29b2fdb3 \
+    --hash=sha256:2454ada8209bbde97065453a6ca488884bbb263e623d35ba183821317a58b46f \
+    --hash=sha256:1b1f136d74f411f587b07c076149c4436a169dc19532e587460d9ced24adcc13 \
+    --hash=sha256:418e7a5ec02a7056d3a4f0c0e7ea81df374205f25f4720bb0e84189aa5fd2515 \
+    --hash=sha256:05a6052c6a9f17ff78ba78f8e6eb1d777d25db3b763343a1ae89a7a8670386dd
 cffi==1.11.5 \
     --hash=sha256:1b0493c091a1898f1136e3f4f991a784437fac3673780ff9de3bcf46c80b6b50 \
     --hash=sha256:87f37fe5130574ff76c17cab61e7d2538a16f843bb7bca8ebbc4b12de3078596 \