Update INSTALL.md
Update INSTALL.md

Former-commit-id: 85a022f87578405b206c7394e2828cd9b38e4f8c
shuheik/dynet,clab/cnn,danielhers/dynet,danielhers/dynet,xunzhang/dynet,shuheik/dynet,shuheik/dynet,clab/dynet,xunzhang/dynet,clab/dynet,shuheik/dynet,xunzhang/dynet,danielhers/dynet,clab/cnn,danielhers/dynet,chunyang-wen/dynet,xunzhang/dynet,shuheik/dynet,shuheik/dynet,clab/dynet,chunyang-wen/dynet,danielhers/dynet,chunyang-wen/dynet,shuheik/dynet,clab/dynet,chunyang-wen/dynet,danielhers/dynet,clab/cnn,clab/dynet,clab/dynet,clab/dynet,danielhers/dynet