Remove upper bound on boto3 version

I can't find a reason for this for limiting us to 1.5 or earlier, and
it's leading to conflicts with other libraries that require newer
versions of botocore.

Author: phobologic

setup.py

@@ -8,7 +8,7 @@
 install_requires = [
     "troposphere>=1.9.0",
     "botocore>=1.6.0",
-    "boto3>=1.3.1,<1.5.0",
+    "boto3>=1.3.1",
     "PyYAML~=3.12",
     "awacs>=0.6.0",
     "formic~=0.9b",