fix wrong tag on docker image (#193)

Was tagging the image with "latest", should be the CPU type

.travis.yml

@@ -31,7 +31,7 @@ script:
   - echo "about to execute build inside docker"
   - docker exec build df -h
   - docker exec build compile-onnx-mlir.sh
-  - docker commit build onnxmlirczar/onnx-mlir-build:latest
+  - docker commit build onnxmlirczar/onnx-mlir-build:$TRAVIS_CPU_ARCH
 after_success: 
   - if [ $TRAVIS_PULL_REQUEST == false ] && [ $TRAVIS_BRANCH == "master" ]; then
             echo "Pushing new build to docker hub";