adding redis 4 to travis

.travis.yml

@@ -20,6 +20,7 @@ jobs:
             - libgif-dev
             - libpango1.0-dev
             - g++-4.9
+            - wget
 
       before_install:
         # Add custom PPAs from cartodb
@@ -55,7 +56,7 @@ jobs:
         - echo -e "# TYPE  DATABASE        USER            ADDRESS                 METHOD \nlocal   all             postgres                                trust\nlocal   all             all                                     trust\nhost    all             all             127.0.0.1/32            trust" \
           | sudo tee /etc/postgresql/9.5/main/pg_hba.conf
         - sudo /etc/init.d/postgresql restart 9.5
-        
+
         - createdb template_postgis
         - createuser publicuser
         - psql -c "CREATE EXTENSION postgis" template_postgis
@@ -64,6 +65,15 @@ jobs:
         - curl -o- -L https://yarnpkg.com/install.sh | bash -s -- --version 0.27.5	
         - export PATH="$HOME/.yarn/bin:$PATH"
 
+        # instal redis 4
+        - wget http://download.redis.io/releases/redis-4.0.8.tar.gz
+        - tar xvzf redis-4.0.8.tar.gz
+        - cd redis-4.0.8
+        - make
+        - sudo make install
+        - cd ..
+        - rm redis-4.0.8.tar.gz
+
       env:
         - NPROCS=1 JOBS=1 PGUSER=postgres CXX=g++-4.9