tox: Simplify robotframework version constraints

Author: userzimmermann

tox.ini

@@ -12,11 +12,11 @@ envlist =
 
 [testenv]
 deps =
-    robot2.8: robotframework>=2.8,<2.9
-    robot2.8py3: robotframework-python3>=2.8,<2.9
-    robot2.9: robotframework>=2.9,<3.0
-    robot2.9py3: robotframework-python3>=2.9,<3.0
-    robot3.0: robotframework>=3.0,<3.1
+    robot2.8: robotframework~=2.8.0
+    robot2.8py3: robotframework-python3~=2.8.0
+    robot2.9: robotframework~=2.9.0
+    robot2.9py3: robotframework-python3~=2.9.0
+    robot3.0: robotframework~=3.0.0
     py{27,py}: robotremoteserver
     pytest