use trusty for testing, to have a recent FUSE

.travis/install.sh

@@ -32,6 +32,7 @@ if [[ "$(uname -s)" == 'Darwin' ]]; then
     python -m pip install --user 'virtualenv<14.0'
 else
     pip install 'virtualenv<14.0'
+    sudo apt-get update
     sudo apt-get install -y liblz4-dev
     sudo apt-get install -y libacl1-dev
 fi