Minor fix for code block.
Minor fix for code block.


Former-commit-id: afc11f47cc7e9c21ea606c36a79baa271bcf26bb
danielhers/dynet,danielhers/dynet,clab/dynet,danielhers/dynet,clab/dynet,clab/dynet,xunzhang/dynet,danielhers/dynet,shuheik/dynet,clab/dynet,danielhers/dynet,clab/dynet,shuheik/dynet,clab/cnn,shuheik/dynet,clab/dynet,danielhers/dynet,danielhers/dynet,shuheik/dynet,shuheik/dynet,clab/cnn,xunzhang/dynet,clab/dynet,shuheik/dynet,xunzhang/dynet,chunyang-wen/dynet,shuheik/dynet,chunyang-wen/dynet,clab/cnn,chunyang-wen/dynet,xunzhang/dynet,chunyang-wen/dynet