fix travis doc folder name

Author: CJ-Wright

.travis.yml

@@ -40,7 +40,7 @@ script:
   - |
     if [ $TRAVIS_PYTHON_VERSION = "3.6" ]; then
       conda install --yes --file requirements/docs.txt
-      cd docs
+      cd doc
       make html
       cd ..
       doctr deploy . --built-docs ./docs/_build/html;