chore: add --frozen-lockfile to CI/CD 'yarn install' invocations

.travis.yml

@@ -17,7 +17,7 @@ script:
   # Building the Docker image
   - docker build --pull --build-arg BUILD_TIMESTAMP=$(date -u +'%Y-%m-%dT%H:%M:%SZ') --build-arg COMMIT_ID="${TRAVIS_COMMIT}" -t "jsii/superchain:nightly" ./superchain
   # Building jsii itself within the Docker image
-  - docker run --rm -it --network=host -v ${PWD}:${PWD} -w ${PWD} jsii/superchain:nightly bash -c "yarn install && yarn build && yarn test"
+  - docker run --rm -it --network=host -v ${PWD}:${PWD} -w ${PWD} jsii/superchain:nightly bash -c "yarn install --frozen-lockfile && yarn build && yarn test"
   # Make sure the build did not change the source tree
   - git update-index --refresh
   - git diff-index --exit-code --stat HEAD

buildspec.yaml

@@ -5,7 +5,7 @@ phases:
     commands:
       # Temporarily - install yarn if it's not there already
       - yarn --version || npm install --global yarn
-      - yarn install
+      - yarn install --frozen-lockfile
   pre_build:
     commands:
       - yarn fetch-dotnet-snk