MAINT: Upgrade six, futures, requests-futures, piprot versions

Upgrade six 1.9.0 -> 1.10.0 in requirements.txt, and futures 3.0.3 ->
3.0.5, requests-futures 0.9.5 -> 0.9.7, and piprot 0.9.1 -> 0.9.6 in
requirements_dev.txt.

etc/requirements.txt

@@ -20,7 +20,7 @@ patsy==0.4.0
 statsmodels==0.6.1
 
 python-dateutil==2.4.2
-six==1.9.0
+six==1.10.0
 
 # For fetching remote data
 requests==2.9.1

etc/requirements_dev.txt

@@ -54,9 +54,9 @@ matplotlib==1.4.3
 Markdown==2.6.2
 
 # Checking for old PIP packages
-futures==3.0.3
-requests-futures==0.9.5
-piprot==0.9.1
+futures==3.0.5
+requests-futures==0.9.7
+piprot==0.9.6
 
 # For asset db management
 alembic==0.7.7