Fix typos in PyCNN tutorial
Fix typos in PyCNN tutorial

Former-commit-id: 7f247753df53a624b945cdb5745b787c16c90da4
clab/dynet,chunyang-wen/dynet,danielhers/dynet,chunyang-wen/dynet,shuheik/dynet,clab/dynet,clab/dynet,danielhers/dynet,clab/cnn,shuheik/dynet,clab/cnn,clab/dynet,shuheik/dynet,chunyang-wen/dynet,xunzhang/dynet,clab/dynet,danielhers/dynet,danielhers/dynet,chunyang-wen/dynet,shuheik/dynet,clab/dynet,shuheik/dynet,xunzhang/dynet,danielhers/dynet,xunzhang/dynet,clab/cnn,shuheik/dynet,clab/dynet,xunzhang/dynet,danielhers/dynet,danielhers/dynet,shuheik/dynet