Update requirements-dev.txt

Update versions of required packages.

Author: renanrodrigo

requirements-dev.txt

@@ -1,13 +1,15 @@
 # For developers, the packages below are required.
-tox >= 2.6.0
+tox ~= 2.7
 
 # For running doctests (during "python setup.py test")
 Sphinx >= 1.4.5
 sphinx_bootstrap_theme
 
 # Linters
-pylama-pylint >= 3.0.1
-radon >= 1.4.0
+pydocstyle ~= 1.1
+pylama ~= 7.3
+pylama_pylint ~= 3.0
+radon ~= 1.5
 
 # Code coverage
 coverage >= 4.1