fixed gpu import in pydynet
fixed gpu import in pydynet


Former-commit-id: 172bcec05cf4062c462c420ef249db610a9744b0
danielhers/dynet,shuheik/dynet,shuheik/dynet,clab/dynet,danielhers/dynet,danielhers/dynet,shuheik/dynet,xunzhang/dynet,xunzhang/dynet,xunzhang/dynet,shuheik/dynet,clab/cnn,clab/dynet,clab/dynet,danielhers/dynet,danielhers/dynet,clab/cnn,xunzhang/dynet,clab/dynet,chunyang-wen/dynet,danielhers/dynet,chunyang-wen/dynet,shuheik/dynet,danielhers/dynet,clab/cnn,clab/dynet,clab/dynet,shuheik/dynet,shuheik/dynet,chunyang-wen/dynet,clab/dynet,chunyang-wen/dynet