Add libboost-regex-dev, without which Travis tests fail
Add libboost-regex-dev, without which Travis tests fail


Former-commit-id: b3b32821aed55993279bec703e79990a4308dafb
clab/dynet,danielhers/dynet,shuheik/dynet,clab/dynet,danielhers/dynet,danielhers/dynet,xunzhang/dynet,shuheik/dynet,clab/cnn,clab/dynet,shuheik/dynet,shuheik/dynet,clab/dynet,chunyang-wen/dynet,clab/dynet,shuheik/dynet,clab/cnn,clab/cnn,clab/dynet,chunyang-wen/dynet,danielhers/dynet,shuheik/dynet,shuheik/dynet,chunyang-wen/dynet,xunzhang/dynet,danielhers/dynet,xunzhang/dynet,danielhers/dynet,clab/dynet,danielhers/dynet,xunzhang/dynet,chunyang-wen/dynet