add tests for gcc 4.8, bump to 3.0

.github/workflows/ci.yml

@@ -16,6 +16,7 @@ jobs:
       fail-fast: false
       matrix:
         name: [
+          ubuntu-18.04-gcc-4.8,
           ubuntu-18.04-gcc-5,
           ubuntu-18.04-gcc-6,
           ubuntu-18.04-gcc-7,
@@ -45,6 +46,11 @@ jobs:
         ]
 
         include:
+          - name: ubuntu-18.04-gcc-4.8
+            os: ubuntu-18.04
+            compiler: gcc
+            version: "4.8"
+
           - name: ubuntu-18.04-gcc-5
             os: ubuntu-18.04
             compiler: gcc