add versions for dependencies and drop python 3.5

pyproject.toml

@@ -18,8 +18,8 @@ classifiers = [
     "Intended Audience :: Developers",
     "License :: OSI Approved :: BSD License",
     "Programming Language :: Python :: 2.7",
-    "Programming Language :: Python :: 3.4",
     "Programming Language :: Python :: 3.6",
+    "Programming Language :: Python :: 3.7",
     "Programming Language :: Python :: 3.8",
     "Topic :: Software Development :: Libraries :: Python Modules",
     "Topic :: System :: Systems Administration :: Authentication/Directory",
@@ -33,8 +33,8 @@ repository = "https://github.com/pyradius/pyrad"
 
 [tool.poetry.dependencies]
 python = "^2.7 || ^3.6"
-six = "*"
-netaddr = "*"
+six = "^1.15.0"
+netaddr = "^0.8"
 
 [tool.poetry.dev-dependencies]
 nose = "^0.10.0b1"