Fix dead links causing failed doc build
Fix dead links causing failed doc build

Former-commit-id: bcea61eab911d42c900d44dce2575a034c791c5c
danielhers/dynet,shuheik/dynet,xunzhang/dynet,shuheik/dynet,danielhers/dynet,clab/dynet,shuheik/dynet,clab/cnn,xunzhang/dynet,shuheik/dynet,chunyang-wen/dynet,danielhers/dynet,chunyang-wen/dynet,chunyang-wen/dynet,danielhers/dynet,xunzhang/dynet,chunyang-wen/dynet,clab/dynet,clab/dynet,clab/cnn,danielhers/dynet,shuheik/dynet,clab/dynet,clab/dynet,danielhers/dynet,xunzhang/dynet,shuheik/dynet,clab/dynet,clab/dynet,shuheik/dynet,danielhers/dynet,clab/cnn