Update sphinx from 1.5.2 to 1.5.3

requirements/docs.txt

@@ -7,9 +7,9 @@ Pygments==2.2.0 \
     --hash=sha256:78f3f434bcc5d6ee09020f92ba487f95ba50f1e3ef83ae96b9d5ffa1bab25c5d \
     --hash=sha256:dbae1046def0efb574852fab9e90209b23f556367b5a320c0bcb871c77c3e8cc
 # Sphinx is required by sphinxcontrib-httpdomain
-Sphinx==1.5.2 \
-    --hash=sha256:57c8636e1d23f6c01fb19911a8f255f1b4934ba69feb55bd4dd0f097ebb04f05 \
-    --hash=sha256:049c48393909e4704a6ed4de76fd39c8622e165414660bfb767e981e7931c722
+Sphinx==1.5.3 \
+    --hash=sha256:2809b2ab81906483b47c9d7e28740e3b69c160617f33d7aa11dc4ae376fd04d9 \
+    --hash=sha256:4f6b257bea61ee6454538dcdb9e8cf56470b4dc6c4f9f750de4aedc57557814f
 # alabaster is required by Sphinx
 alabaster==0.7.9 \
     --hash=sha256:d3e64a74919373d6d4d1d36bd717206584cb64cbb0532dfce3bc2081cba6817b \