Add script to install cryptography to the build.

Fixes: candango#84

.travis.yml

@@ -9,6 +9,7 @@ python:
 install:
   - "pip install -r requirements/basic.txt"
   - "pip install -r requirements/tests.txt"
+  - ./scripts/install_cryptography.sh
   - "go get -u github.com/letsencrypt/pebble/..."
   - |
     (

scripts/install_cryptography.sh

@@ -0,0 +1,14 @@
+#!/bin/bash
+
+export PYTHONPATH=$PYTHONPATH:.
+
+PYTHON_VERSION=`python -c 'import sys; print(sys.version_info.minor)'`
+
+if [ $PYTHON_VERSION -eq 5 ]; then
+    pip install -r requirements/cryptography_legacy.txt;
+    exit;
+else
+    pip install -r requirements/cryptography.txt;
+    exit;
+fi
+exit 0;