Update/fix build (cereal optional)

.travis.yml

@@ -1,46 +1,39 @@
-dist: trusty
-
 language: cpp
 
 matrix:
   include:
-    - name: "GCC 4.8 (Linux)"  # GCC 4.8.5 & CMake 3.9.2
+    - name: "GCC 4.8 (Linux)"  # GCC 4.8.5 & CMake 3.12.4
       os: linux
+      dist: xenial
       addons:
         apt:
           sources:
             - ubuntu-toolchain-r-test
           packages:
             - g++-4.8
-            - cmake
       env:
         - SET_COMPILER="export CC=gcc-4.8 && export CXX=g++-4.8"
 
-    - name: "Clang 3.5 (Linux)"  # Clang 3.5.0 & CMake 3.9.2
+    - name: "Clang 3.5 (Linux)"  # Clang 3.5.0 & CMake 3.12.4
       os: linux
+      dist: xenial
       addons:
         apt:
-          sources:
-            - llvm-toolchain-trusty-3.5
           packages:
             - clang-3.5
-            - cmake
       env:
         - SET_COMPILER="export CC=clang-3.5 && export CXX=clang++-3.5"
 
-    - name: "Clang Xcode 9.0 (OSX)"  # Clang 9.0.0 & CMake 3.9.2
+    - name: "Clang Xcode 9.4 (OSX)"  # Clang 9.4.1 & CMake 3.15.5
       os: osx
-      osx_image: xcode9
+      osx_image: xcode9.4
 
 before_install:
   - eval "${SET_COMPILER}"
-  - git clone https://github.com/google/googletest && cd googletest && mkdir build && cd build && git checkout 703bd9c
-  - cmake -DCMAKE_CXX_FLAGS="-std=c++11" .. && make && sudo make install
-  - cd ../../
 
 install:
   - mkdir build && cd build
-  - cmake -Dspoa_build_executable=ON -Dspoa_build_tests=ON -DCMAKE_BUILD_TYPE=Release .. && make
+  - cmake -DCMAKE_BUILD_TYPE=Release .. && make
 
 script:
   - ./bin/spoa --version