fix

.travis.yml

@@ -92,7 +92,7 @@ script:
 - $HOME/gopath/bin/goveralls -coverprofile=merge.cov -service=travis-ci
 
 # Docker build
-- docker build --build-args COMMIT=$TRAVIS_COMMIT -t mlab/tcpinfo .
+- docker build --build-arg COMMIT=$TRAVIS_COMMIT -t mlab/tcpinfo .
 
 #################################################################################
 # Deployment Section

Dockerfile

@@ -14,8 +14,9 @@ RUN apk update && apk add bash git unzip
 WORKDIR /go/src/github.com/m-lab
 RUN git clone https://github.com/m-lab/tcp-info
 WORKDIR tcp-info
-# allows override with --build-args COMMIT=branch-or-commit, defaults to $TRAVIS_COMMIT or master
-ARG COMMIT=${COMMIT}
+# allows override with --build-args COMMIT=branch-or-commit, defaults to master
+ARG COMMIT=master
+RUN echo $COMMIT
 RUN git checkout $COMMIT
 
 # List all of the go imports, excluding any in this repo, and run go get to import them.