Disable arm64-graviton2 for now [ci skip]

Author: probonopd

.travis.yml

@@ -3,7 +3,9 @@ dist: xenial
 virt: vm
 group: edge
 arch:
-    - arm64-graviton2
+    # The following seems not to work; still runs on an amd64 host;
+    # maybe because we have not been migrated from travis-ci.org to travis-ci.com yet?
+    # arm64-graviton2
     - amd64
 
 os: linux