Remove some failing ARM 64, and add an environment variable

Env variable for better report of travis failure in the UI or the builds
are otherwise impossible to  distinguish.

.travis.yml

@@ -72,23 +72,16 b' matrix:'
     - arch: arm64
       python: "3.7"
       dist: xenial
+      env: ARM64=True
       sudo: true
     - arch: amd64
       python: "3.8-dev"
       dist: xenial
       sudo: true
-    - arch: arm64
-      python: "3.8-dev"
-      dist: xenial
-      sudo: true
     - arch: amd64
       python: "3.7-dev"
       dist: xenial
       sudo: true
-    - arch: arm64
-      python: "3.7-dev"
-      dist: xenial
-      sudo: true
     - arch: amd64
       python: "nightly"
       dist: xenial
@@ -96,6 +89,7 b' matrix:'
     - arch: arm64
       python: "nightly"
       dist: bionic
+      env: ARM64=True
       sudo: true
     - os: osx
       language: generic