update .travis.yml

Author: Vadym Slizov

.travis.yml

@@ -3,15 +3,11 @@ branches:
   only:
     - master
 before_script:
-  - go get -u gotest.tools/assert
-  - go get -u golang.org/x/tools/cmd/goyacc
-  - go get -u github.com/pkg/profile
-  - go get -u github.com/cznic/golex/lex
-  - go get -u github.com/yookoala/realpath
+  - env GO111MODULE=on go mod download
   - curl -L https://codeclimate.com/downloads/test-reporter/test-reporter-latest-linux-amd64 > ./cc-test-reporter
   - chmod +x ./cc-test-reporter
   - ./cc-test-reporter before-build
 script:
-  - go test -coverprofile c.out ./...
+  - env GO111MODULE=on go test -coverprofile c.out ./...
 after_script:
   - ./cc-test-reporter after-build --coverage-input-type gocov --exit-code $TRAVIS_TEST_RESULT