Update tests.sh

tests.sh

@@ -226,12 +226,8 @@ internal_install_python_deps() {
   if [ "$TRAVIS" != "true" ]; then
     return;
   fi
-  # Install tox (OS X doesn't have pip).
-  if [ $(uname -s) == "Darwin" ]; then
-    sudo easy_install tox
-  else
-    sudo pip install tox
-  fi
+  # install tox
+  sudo pip install tox
   # Only install Python2.6/3.x on Linux.
   if [ $(uname -s) == "Linux" ]; then
     sudo apt-get install -y python-software-properties # for apt-add-repository