Added missing import in conf.py
Added missing import in conf.py

Former-commit-id: 2bf517f27b77320f788a9ed1e7fab19b07c59c0c
danielhers/dynet,chunyang-wen/dynet,xunzhang/dynet,clab/dynet,clab/cnn,danielhers/dynet,danielhers/dynet,shuheik/dynet,xunzhang/dynet,clab/dynet,shuheik/dynet,chunyang-wen/dynet,clab/dynet,clab/dynet,shuheik/dynet,shuheik/dynet,clab/dynet,shuheik/dynet,chunyang-wen/dynet,danielhers/dynet,danielhers/dynet,danielhers/dynet,clab/cnn,clab/dynet,clab/dynet,shuheik/dynet,xunzhang/dynet,chunyang-wen/dynet,xunzhang/dynet,danielhers/dynet,shuheik/dynet,clab/cnn