Upgrade requirements to build on ubuntu

.travis.yml

@@ -9,9 +9,9 @@ matrix:
           sources:
             - ubuntu-toolchain-r-test
           packages:
-            - g++-8
+            - g++-9
       env:
-        - MATRIX_EVAL="CC=gcc-8 && CXX=g++-8"
+        - MATRIX_EVAL="CC=gcc-9 && CXX=g++-9"
       compiler:
         - gcc
 before_install:
@@ -19,7 +19,7 @@ before_install:
 - sudo apt-get install build-essential cmake libboost-all-dev libconfig++-dev libavcodec-dev libavutil-dev libavformat-dev ffmpeg libgraphicsmagick++1-dev libpstreams-dev libconfig++-dev libpstreams-dev libtag1-dev
 - git clone https://github.com/emweb/wt.git wt
 - pushd wt;
-- git checkout 4.1.0
+- git checkout 4.2.1
 - cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/usr && sudo make install
 - popd
 script: cmake -DCMAKE_BUILD_TYPE=Release . && make && make test