Fixed build error on Travis

.travis.sh

@@ -40,10 +40,6 @@ echo "$TRAVIS_BRANCH" | grep -qvE "^[0-9.]+$" && exit 0; :;
 # Install dependencies for release build
 pip install --user wheel twine
 
-# Fix SSL warnings for Python > 2.7.9
-# https://urllib3.readthedocs.io/en/latest/user-guide.html#ssl-py2
-pip install --user urllib3[secure]
-
 # Build and install theme and Docker image
 python setup.py build sdist bdist_wheel --universal
 docker build -t $TRAVIS_REPO_SLUG .

requirements.txt

@@ -18,6 +18,10 @@
 # FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 # IN THE SOFTWARE.
 
+# Direct dependencies
 mkdocs>=0.17.1
 Pygments>=2.2
 pymdown-extensions>=3.4
+
+# Temporary fix for build errors on Travis
+tornado<5