travis, update build kernel

.travis.yml

@@ -1,3 +1,6 @@
+dist: trusty
+sudo: required
+
 language: cpp
 compiler:
   - gcc
@@ -10,12 +13,12 @@ before_install:
   - git submodule update --init --recursive
   - sudo add-apt-repository ppa:ubuntu-toolchain-r/test -y
   - sudo apt-get update -qq
-  - sudo apt-get install -y libpcap-dev linux-headers-3.13.0-36-generic cmake
+  - sudo apt-get install -y libpcap-dev linux-headers-4.4.0-75-generic cmake
   - sudo apt-get install -y doxygen graphviz
   - if [ "$CXX" = "clang++" ]; then sudo apt-get install -qq libstdc++-4.8-dev; fi
   - if [ "$CXX" = "g++" ]; then sudo apt-get install -qq g++-4.8; fi
   - if [ "$CXX" = "g++" ]; then export CXX="g++-4.8" CC="gcc-4.8"; fi
-env: BUILD_KERNEL=3.13.0-36-generic
+env: BUILD_KERNEL=4.4.0-75-generic
 install:
 script:
   - ./travis.sh