travis: added arm64 test.

.travis.yml

@@ -6,6 +6,10 @@ matrix:
     - language: c
       compiler: clang
       script: make
+    - arch: arm64
+      language: c
+      compiler: gcc
+      script: make arm_neon=1 aarch64=1
     - language: python
       python: "2.7"
       before_install: pip install cython