Bump default base image to Ubuntu 20.04.

README.md

@@ -101,7 +101,7 @@ Image build options:
 
 Additional options:
   --base_image BASE_IMAGE
-                        The base image. (centos:8 is supported too) (default: ubuntu:19.10)
+                        The base image. (centos:8 is supported too) (default: ubuntu:20.04)
   --compiler COMPILER   The compiler to use. Possible options: off, gcc, clang (default: gcc)
   --compiler_version COMPILER_VERSION
                         Compiler version. (default: )

ogscm/cli_args.py

@@ -129,7 +129,7 @@ class Cli_Args(argparse.ArgumentParser):
         switches_g = self.add_argument_group('Additional options')
         switches_g.add_argument('--base_image',
                                 type=str,
-                                default='ubuntu:19.10',
+                                default='ubuntu:20.04',
                                 help='The base image. (centos:8 is supported too)')
         switches_g.add_argument(
             '--compiler',