Fixed docker file to use vendoring.

Dockerfile

@@ -4,13 +4,11 @@ ENV SOURCE_DIR /relations-api-src
 
 COPY *.go *.git $SOURCE_DIR/
 COPY relations/*.go $SOURCE_DIR/relations/
+COPY vendor/vendor.json $SOURCE_DIR/vendor/
 
 RUN apk add --no-cache  --update bash ca-certificates \
   && apk --no-cache --virtual .build-dependencies add git go libc-dev \
   && cd $SOURCE_DIR \
-  && export GOPATH=/gopath \
-  && go get -u github.com/kardianos/govendor \
-  && $GOPATH/bin/govendor sync \
   && BUILDINFO_PACKAGE="github.com/Financial-Times/service-status-go/buildinfo." \
   && VERSION="version=$(git describe --tag --always 2> /dev/null)" \
   && DATETIME="dateTime=$(date -u +%Y%m%d%H%M%S)" \
@@ -19,10 +17,13 @@ RUN apk add --no-cache  --update bash ca-certificates \
   && BUILDER="builder=$(go version)" \
   && LDFLAGS="-X '"${BUILDINFO_PACKAGE}$VERSION"' -X '"${BUILDINFO_PACKAGE}$DATETIME"' -X '"${BUILDINFO_PACKAGE}$REPOSITORY"' -X '"${BUILDINFO_PACKAGE}$REVISION"' -X '"${BUILDINFO_PACKAGE}$BUILDER"'" \
   && cd .. \
+  && export GOPATH=/gopath \
+  && go get -u github.com/kardianos/govendor \
   && REPO_PATH="github.com/Financial-Times/relations-api" \
   && mkdir -p $GOPATH/src/${REPO_PATH} \
   && cp -r $SOURCE_DIR/* $GOPATH/src/${REPO_PATH} \
   && cd $GOPATH/src/${REPO_PATH} \
+  && $GOPATH/bin/govendor sync \
   && go get ./... \
   && echo ${LDFLAGS} \
   && go build -ldflags="${LDFLAGS}" \