Use bionic for builds

Author: TheAssassin

.github/workflows/main.yml

@@ -11,7 +11,7 @@ on:
 jobs:
   appimage-x86_64:
     name: AppImage x86_64
-    runs-on: ubuntu-16.04
+    runs-on: ubuntu-18.04
     env:
       ARCH: x86_64
     steps:
@@ -28,7 +28,7 @@ jobs:
 
   appimage-i386:
     name: AppImage i386
-    runs-on: ubuntu-16.04
+    runs-on: ubuntu-18.04
     env:
       ARCH: i386
     steps: