Remove config for Travis CI

It is outdated and using an unsupported Ubuntu distribution.

.travis.yml

@@ -1,13 +0,0 @@
-language: cpp
-sudo: required
-dist: trusty
-before_script:
- - sudo apt-get install -yq --no-install-suggests software-properties-common
- - sudo add-apt-repository ppa:ubuntu-toolchain-r/test -y
- - sudo apt-get update -y
- - sudo apt-get install -yq --no-install-suggests gcc-5 g++-5 liblmdb-dev libboost-dev libboost-serialization-dev
- - sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-5 60 --slave /usr/bin/g++ g++ /usr/bin/g++-5
- - sudo -E apt-get -yq --no-install-suggests --no-install-recommends --force-yes install make 
-script:
- - make
- - make check