Update workflows

Author: jdavidberger

.github/workflows/build_wheels.yml

@@ -16,7 +16,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-18.04, windows-latest]
+        os: [ubuntu-20.04, windows-latest]
 
     # Steps represent a sequence of tasks that will be executed as part of the job
     steps:

.github/workflows/cmake.yml

@@ -17,9 +17,9 @@ jobs:
       fail-fast: false
       matrix:
         build_type: [Release]
-        os: [ubuntu-18.04, windows-latest]
+        os: [ubuntu-20.04, windows-latest]
         include:
-        - os: ubuntu-18.04
+        - os: ubuntu-20.04
           build_type: Debug
           config_flags: "-DUSE_ASAN=ON"
           deps: libasan6

.github/workflows/publish-source.yml

@@ -8,7 +8,7 @@ on:
 
 jobs:
   gather-source:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     steps:
     - uses: actions/checkout@v2
       with: