Airflow theme v0.0.5 (#428)

Sphinx 1.8 was where add_stylesheet was renamed to add_css_file, so just
for the sake of completeness I have specified it
diff --git a/sphinx_airflow_theme/setup.py b/sphinx_airflow_theme/setup.py
index 1b253ed..d77f724 100644
--- a/sphinx_airflow_theme/setup.py
+++ b/sphinx_airflow_theme/setup.py
@@ -64,7 +64,7 @@
         ]
     },
     install_requires=[
-        'sphinx'
+        'sphinx>=1.8'
     ],
     tests_require=[],
     extras_require={
diff --git a/sphinx_airflow_theme/sphinx_airflow_theme/__init__.py b/sphinx_airflow_theme/sphinx_airflow_theme/__init__.py
index dec1ff7..27db9a7 100644
--- a/sphinx_airflow_theme/sphinx_airflow_theme/__init__.py
+++ b/sphinx_airflow_theme/sphinx_airflow_theme/__init__.py
@@ -18,7 +18,7 @@
 from os import path
 from sphinx.application import Sphinx
 
-__version__ = '0.0.4'
+__version__ = '0.0.5'
 __version_full__ = __version__