Use hard selenium version of 2.53.6

requirements.txt

@@ -1,6 +1,6 @@
 pip>=8.1.2
 setuptools>=28.2.0
-selenium>=2.53.6
+selenium==2.53.6
 nose>=1.3.7
 pytest>=3.0.2
 six>=1.10.0

server_requirements.txt

@@ -1,6 +1,6 @@
 pip>=8.1.2
 setuptools>=28.2.0
-selenium>=2.53.6
+selenium==2.53.6
 nose>=1.3.7
 pytest>=3.0.2
 six>=1.10.0

setup.py

@@ -16,7 +16,7 @@ setup(
     install_requires=[
         'pip>=8.1.2',
         'setuptools>=28.2.0',
-        'selenium>=2.53.6',
+        'selenium==2.53.6',
         'nose>=1.3.7',
         'pytest>=3.0.2',
         'six>=1.10.0',