vagrant: update to Python 3.5.5 (for binary builds)

(cherry picked from commit 6b44531330b2373ed8f8c8dc3c4ef5ac35c25f46)

Vagrantfile

@@ -236,7 +236,7 @@ def install_pythons(boxname)
     pyenv install 3.4.0  # tests
     pyenv install 3.5.0  # tests
     pyenv install 3.6.0  # tests
-    pyenv install 3.5.4  # binary build, use latest 3.5.x release
+    pyenv install 3.5.5  # binary build, use latest 3.5.x release
     pyenv rehash
   EOF
 end
@@ -254,8 +254,8 @@ def build_pyenv_venv(boxname)
     . ~/.bash_profile
     cd /vagrant/borg
     # use the latest 3.5 release
-    pyenv global 3.5.4
-    pyenv virtualenv 3.5.4 borg-env
+    pyenv global 3.5.5
+    pyenv virtualenv 3.5.5 borg-env
     ln -s ~/.pyenv/versions/borg-env .
   EOF
 end