Update sphinx from 1.7.3 to 1.7.4

requirements/docs.txt

@@ -9,9 +9,9 @@ Pygments==2.2.0 \
     --hash=sha256:78f3f434bcc5d6ee09020f92ba487f95ba50f1e3ef83ae96b9d5ffa1bab25c5d \
     --hash=sha256:dbae1046def0efb574852fab9e90209b23f556367b5a320c0bcb871c77c3e8cc
 # Sphinx is required by sphinxcontrib-httpdomain
-Sphinx==1.7.3 \
-    --hash=sha256:3aded1a355f662547b8a948131f3faecbc3dea8951847fe0ee4c59689f8220b2 \
-    --hash=sha256:9495a1f78c13d0a725ab8104e923e9663519ecc04552aa4a8f684c2da355443d
+Sphinx==1.7.4 \
+    --hash=sha256:2e7ad92e96eff1b2006cf9f0cdb2743dacbae63755458594e9e8238b0c3dc60b \
+    --hash=sha256:e9b1a75a3eae05dded19c80eb17325be675e0698975baae976df603b6ed1eb10
 # alabaster is required by Sphinx
 alabaster==0.7.10 \
     --hash=sha256:2eef172f44e8d301d25aff8068fddd65f767a3f04b5f15b0f4922f113aa1c732 \