Build on focal, use arm64-graviton2 for aarch64 tests

Author: mayeut

.travis.yml

@@ -1,5 +1,5 @@
 os: linux
-dist: bionic
+dist: focal
 language: python
 
 jobs:
@@ -9,7 +9,9 @@ jobs:
   - python: "3.8"
   - python: "3.9"
   - python: "3.7"
-    arch: arm64
+    arch: arm64-graviton2
+    virt: vm
+    group: edge
   - python: "3.7"
     arch: ppc64le
   - python: "3.7"