fix warning
fix warning


Former-commit-id: eec52683916d063a14e8d111ce21254f90bf9278
shuheik/dynet,danielhers/dynet,chunyang-wen/dynet,chunyang-wen/dynet,xunzhang/dynet,xunzhang/dynet,clab/dynet,chunyang-wen/dynet,shuheik/dynet,danielhers/dynet,shuheik/dynet,clab/dynet,danielhers/dynet,danielhers/dynet,shuheik/dynet,clab/dynet,shuheik/dynet,danielhers/dynet,chunyang-wen/dynet,shuheik/dynet,clab/dynet,danielhers/dynet,shuheik/dynet,clab/cnn,clab/dynet,clab/cnn,xunzhang/dynet,clab/dynet,clab/cnn,danielhers/dynet,clab/dynet,xunzhang/dynet