Fix matrices in python doc
Fix matrices in python doc


Former-commit-id: 45b83e607ebf0fbb4d79a765c356f5b6f6ff1cea
clab/dynet,shuheik/dynet,shuheik/dynet,clab/dynet,danielhers/dynet,chunyang-wen/dynet,danielhers/dynet,xunzhang/dynet,clab/dynet,chunyang-wen/dynet,danielhers/dynet,clab/cnn,shuheik/dynet,xunzhang/dynet,chunyang-wen/dynet,shuheik/dynet,clab/dynet,clab/cnn,xunzhang/dynet,danielhers/dynet,shuheik/dynet,clab/dynet,danielhers/dynet,shuheik/dynet,danielhers/dynet,chunyang-wen/dynet,xunzhang/dynet,danielhers/dynet,clab/dynet,shuheik/dynet,clab/dynet,clab/cnn