Update install.rst (#1526)
Update install.rst (#1526)

Change ./examples/train_xor to ./examples/xor.
Running ./examples/train_xor produces an error "No such file or directory"
danielhers/dynet,clab/dynet,clab/dynet,danielhers/dynet,clab/dynet,shuheik/dynet,shuheik/dynet,clab/dynet,shuheik/dynet,danielhers/dynet,shuheik/dynet,danielhers/dynet,danielhers/dynet,shuheik/dynet,clab/dynet,shuheik/dynet,shuheik/dynet,danielhers/dynet,clab/dynet,danielhers/dynet,clab/dynet