After deployment, test pip installation from PyPI works (#1076)
After deployment, test pip installation from PyPI works (#1076)

* Add Travis build stage to test pip install after deployment

* Run all Travis jobs on tag

chunyang-wen/dynet,shuheik/dynet,danielhers/dynet,clab/dynet,shuheik/dynet,shuheik/dynet,shuheik/dynet,xunzhang/dynet,danielhers/dynet,danielhers/dynet,xunzhang/dynet,danielhers/dynet,chunyang-wen/dynet,xunzhang/dynet,clab/cnn,danielhers/dynet,clab/cnn,clab/dynet,clab/dynet,shuheik/dynet,clab/dynet,chunyang-wen/dynet,clab/dynet,clab/dynet,clab/cnn,danielhers/dynet,shuheik/dynet,danielhers/dynet,xunzhang/dynet,clab/dynet,chunyang-wen/dynet,shuheik/dynet