Test on ubuntu-18.04, not 16.04 (#889)

* FIX : Test on ubuntu-18.04, not 16.04

ubuntu-16.04 is no longer available on GitHub Actions CI

* FIX : Use ubuntu-latest instead of ubuntu-18.04

* FIX : Use ubuntu-18.04 with the right package repository

	modified:   .github/workflows/test-with-edm.yml
	modified:   ci/edmtool.py

* FIX : Install libsdl2-dev using the ubuntu package manager

	modified:   .github/workflows/test-with-edm.yml

* FIX : Use libsdl1.2, not libsdl2

	modified:   .github/workflows/test-with-edm.yml

.github/workflows/test-with-edm.yml

@@ -15,8 +15,8 @@ jobs:
   test-edm-linux:
     strategy:
       matrix:
-        toolkit: ['null', 'pyqt', 'pyqt5', 'pyside2', 'wx']
-    runs-on: ubuntu-16.04
+        toolkit: ['null', 'pyqt5', 'pyside2', 'wx']
+    runs-on: ubuntu-18.04
     steps:
       - uses: actions/checkout@v2
       - name: Install Qt dependencies for Linux
@@ -27,7 +27,7 @@ jobs:
       - name: Install Wx dependencies for Linux
         run: |
           sudo apt-get update
-          sudo apt-get install libsdl2-2.0-0
+          sudo apt-get install libsdl1.2-dev
         if: matrix.toolkit == 'wx'
       - name: Install GL dependencies for Linux
         run: sudo apt-get install libglu1-mesa-dev

ci/edmtool.py

@@ -190,7 +190,7 @@ def install(runtime, toolkit, environment, source):
         elif sys.platform == "linux":
             # XXX this is mainly for TravisCI workers; need a generic solution
             commands.append(
-                "edm run -e {environment} -- pip install -f https://extras.wxpython.org/wxPython4/extras/linux/gtk3/ubuntu-16.04/ wxPython<4.1"  # noqa: E501
+                "edm run -e {environment} -- pip install -f https://extras.wxpython.org/wxPython4/extras/linux/gtk3/ubuntu-18.04/ wxPython<4.1"  # noqa: E501
             )
         else:
             commands.append(