conf.py: Update year in footer

This will automatically update the year in footer.

Closes coala#582

Author: sambhavkaul

conf.py

@@ -15,6 +15,7 @@
 
 import sys
 import os
+import datetime
 
 import coalib
 
@@ -51,7 +52,8 @@
 
 # General information about the project.
 project = 'coala'
-copyright = '2017, The coala Developers'
+year = datetime.datetime.now().year
+copyright = str(year) + ", The coala Developers"
 author = 'The coala Developers'
 
 # The version info for the project you're documenting, acts as replacement for