[go modules] migrating to go modules

This CL migrates prebid-server to Go Modules getting rid of `dep`.

Issue: #998

.travis.yml

@@ -1,20 +1,13 @@
 language: go
 
 go:
-  - '1.11.1'
+  - '1.11.13'
   - '1.12'
 
 go_import_path: github.com/prebid/prebid-server
 
 env:
-  - DEP_VERSION="0.5.0"
-
-before_install:
-  - curl -L -s https://github.com/golang/dep/releases/download/v${DEP_VERSION}/dep-linux-amd64 -o $GOPATH/bin/dep
-  - chmod +x $GOPATH/bin/dep
-
-install:
-  - $GOPATH/bin/dep ensure
+- GO111MODULE=on
 
 script:
   - "./validate.sh --nofmt --cov --race 10"

Dockerfile

@@ -6,27 +6,20 @@ RUN cd /tmp && \
     wget https://dl.google.com/go/go1.12.7.linux-amd64.tar.gz && \
     tar -xf go1.12.7.linux-amd64.tar.gz && \
     mv go /usr/local
-WORKDIR /go/src/github.com/prebid/prebid-server/
+RUN mkdir -p /app/prebid-server/
+WORKDIR /app/prebid-server/
 ENV GOROOT=/usr/local/go
-ENV GOPATH=/go
-ENV PATH=$GOPATH/bin:$GOROOT/bin:$PATH
-RUN apt-get update && \
-    apt-get install -y git go-dep && \
-    apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
+ENV PATH=$GOROOT/bin:$PATH
 ENV CGO_ENABLED 0
 COPY ./ ./
-RUN dep ensure && \
-    go build .
+RUN go build -mod=vendor .
 
 FROM ubuntu:18.04 AS release
 LABEL maintainer="hans.hjort@xandr.com" 
 WORKDIR /usr/local/bin/
-COPY --from=build /go/src/github.com/prebid/prebid-server/prebid-server .
+COPY --from=build /app/prebid-server/ .
 COPY static static/
 COPY stored_requests/data stored_requests/data
-RUN apt-get update && \
-    apt-get install -y ca-certificates mtr && \
-    apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
 EXPOSE 8000
 EXPOSE 8080
 ENTRYPOINT ["/usr/local/bin/prebid-server"]