Set TravisCI distribution to trusty, fix g++-4.7 issue.
Set TravisCI distribution to trusty, fix g++-4.7 issue.

ufal/morphodita,ufal/morphodita,ufal/morphodita,ufal/morphodita,ufal/morphodita,ufal/morphodita,ufal/morphodita,ufal/morphodita