Run tests on the new LTS 18.04 (#533)

* The new ubuntu LTS is 18.04, dump the version inside CI
* In Ubuntu 18.04 the flex bison lost its headers.
* Now, you can found them inside libfl-dev

Author: Nicolas Cornu

.github/workflows/coreneuron-ci.yml

@@ -28,7 +28,7 @@ jobs:
 
     strategy:
       matrix:
-        os: [ ubuntu-16.04, macOS-10.15 ]
+        os: [ ubuntu-18.04, macOS-10.15 ]
         config:
           - {cmake_option: "-DCORENRN_ENABLE_MPI=ON", documentation: ON }
           - {cmake_option: "-DCORENRN_ENABLE_MPI=OFF"}
@@ -52,7 +52,7 @@ jobs:
       - name: Install apt packages
         if: startsWith(matrix.os, 'ubuntu')
         run: |
-          sudo apt-get install doxygen bison flex libboost-all-dev libopenmpi-dev openmpi-bin python3-dev python3-pip
+          sudo apt-get install doxygen bison flex libboost-all-dev libopenmpi-dev openmpi-bin python3-dev python3-pip libfl-dev
         shell: bash
 
       - name: Install specific apt packages

.github/workflows/coverage.yml

@@ -17,12 +17,12 @@ env:
 
 jobs:
   coverage:
-    runs-on: ubuntu-16.04
+    runs-on: ubuntu-18.04
     name: "Coverage Test"
     steps:
       - name: Install packages
         run: |
-          sudo apt-get install doxygen bison flex libboost-all-dev libopenmpi-dev openmpi-bin python3-dev python3-pip lcov
+          sudo apt-get install doxygen bison flex libboost-all-dev libopenmpi-dev openmpi-bin python3-dev python3-pip lcov libfl-dev
         shell: bash
       - uses: actions/checkout@v2
         with: