*: remove travis config file

We don't use travis anymore, we have GA and CircleCI instead.

.travis.yml

@@ -1,16 +0,0 @@
-language: go
-go:
-  - 1.15.x
-env:
-  - GO111MODULE=on
-install:
-  - go get -v golang.org/x/lint/golint
-  - go mod tidy -v
-script:
-  - golint -set_exit_status ./...
-  - go test -v -race -coverprofile=coverage.txt -covermode=atomic -coverpkg=./pkg/...,./cli/... ./...
-after_success:
-  - bash <(curl -s https://codecov.io/bash)
-matrix:
-  allow_failures:
-    - go: tip