Revert "Add Docker build & push to Travis job" - it's already being built on Docker Hub!

This reverts commit b339a753b5.

.travis.yml

@@ -1,18 +1,6 @@
-sudo: true
-services:
-  - docker
-
 language: go
-
 install: 
   - go get github.com/aquasecurity/kube-bench
 script:
   - go test ./...
   - go build -o kube-bench .
-  
-after_success:
-  - if [ "$TRAVIS_BRANCH" == "master" ]; then
-    docker login -u="$DOCKER_USERNAME" -p="$DOCKER_PASSWORD";
-    docker build -t aquasec/kube-bench .;
-    docker push aquasec/kube-bench;
-    fi