change tox compatibility installs to install extras rather than installing dependencies directly

Author: mattsb42-aws

tox.ini

@@ -11,17 +11,16 @@ commands =
     py.test --cov-report term-missing --cov jose {posargs}
 
 [testenv:compatibility]
-deps =
+extras =
     cryptography
-    pycrypto >=2.6.0, <2.7.0
-    pycryptodome >=3.3.1, <4.0.0
+    pycrypto
+    pycryptodome
 
 [testenv]
 deps =
     pytest
     pytest-cov
     pytest-runner
-    compatibility: {[testenv:compatibility]deps}
 commands_pre =
     # Remove the python-rsa and python-ecdsa backends
     only: pip uninstall -y ecdsa rsa
@@ -42,6 +41,7 @@ extras =
     cryptography: cryptography
     pycryptodome: pycryptodome
     pycrypto: pycrypto
+    compatibility: {[testenv:compatibility]extras}
 
 ; [testenv:flake8]
 ; commands = flake8 jose