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

Abasyoni/dynet,cherryc/dynet,Peilun-Li/dynet,dhgarrette/cnn,kamigaito/cnn,dhgarrette/cnn,cherryc/dynet,Peilun-Li/dynet,mitchellstern/dynet,dhgarrette/cnn,cherryc/dynet,Peilun-Li/dynet,mitchellstern/dynet,Abasyoni/dynet,kamigaito/cnn,Abasyoni/dynet