update letstest reqs (#7809)

I don't fully understand why, but since I updated my macbook to macOS Catalina, the test script currently fails to run for me with the versions of our dependencies we have pinned. Updating the dependencies solves the problem though and you can see Travis also successfully running tests with these new dependencies at https://travis-ci.com/certbot/certbot/builds/150573696.

tests/letstest/requirements.txt

@@ -1,25 +1,19 @@
-asn1crypto==0.24.0
-awscli==1.16.157
-bcrypt==3.1.6
-boto3==1.9.146
-botocore==1.12.147
-cffi==1.12.3
-colorama==0.3.9
-cryptography==2.4.2
-docutils==0.14
-enum34==1.1.6
+bcrypt==3.1.7
+boto3==1.12.7
+botocore==1.15.7
+cffi==1.14.0
+cryptography==2.8
+docutils==0.15.2
+enum34==1.1.9
 Fabric==1.14.1
-futures==3.2.0
-idna==2.8
-ipaddress==1.0.22
-jmespath==0.9.4
-paramiko==2.4.2
-pyasn1==0.4.5
+futures==3.3.0
+ipaddress==1.0.23
+jmespath==0.9.5
+paramiko==2.7.1
 pycparser==2.19
 PyNaCl==1.3.0
-python-dateutil==2.8.0
-PyYAML==3.10
-rsa==3.4.2
-s3transfer==0.2.0
-six==1.12.0
-urllib3==1.24.3
+python-dateutil==2.8.1
+PyYAML==5.3
+s3transfer==0.3.3
+six==1.14.0
+urllib3==1.25.8