[requires.io] dependency update

setup.py

@@ -99,7 +99,7 @@
             "rstcheck>=2.2, <4.0",
             "sphinx_rtd_theme>=0.1.9, <0.3",
             "sphinx-autobuild>=0.5.2, <0.8",
-            "sphinx>=1.3.5, <1.7",
+            "sphinx>=1.7,<1.8",
             "sphinxcontrib-documentedlist>=0.5.0, <0.7",
             "tox>=2.3, <3",
         ],