Pin salt versions correctly

Pins salt versions correctly - were using < which meant we got 3004.1
and 3005 instead of expected versions.

tox.ini

@@ -6,10 +6,10 @@ skipsdist = false
 [testenv]
 passenv = TOXENV, CI, TRAVIS, TRAVIS_*, CODECOV_*
 deps = -r{toxinidir}/tests/requirements.txt
-    v3004.2: salt<3004.2
+    v3004.2: salt==3004.2
     v3004.2: jinja2<3.1
-    v3005.1: salt<3005.1
-    v3006.0: salt<3006.0
+    v3005.1: salt==3005.1
+    v3006.0: salt==3006.0
     py3.7-{cherrypy,tornado}-{v3004.2,v3005.1,v3006.0}: importlib-metadata<5.0.0
     master: git+https://github.com/saltstack/salt.git@master#egg=salt