Run "dep ensure" as part of docker build process

Dockerfile

@@ -1,8 +1,15 @@
 FROM golang:1.10-alpine as builder
-ADD . /go/src/github.com/jimeh/casecmp
+RUN set -e \
+    && apk add --no-cache git \
+    && wget -O - https://github.com/golang/dep/raw/master/install.sh | sh
+
 WORKDIR /go/src/github.com/jimeh/casecmp
-RUN CGO_ENABLED=0 go build -a -o /casecmp \
-    -ldflags "-X main.Version=$(cat VERSION)"
+ADD . /go/src/github.com/jimeh/casecmp
+RUN set -e \
+    && dep ensure \
+    && CGO_ENABLED=0 go build -a -o /casecmp \
+       -ldflags "-X main.Version=$(cat VERSION)"
+
 
 FROM scratch
 COPY --from=builder /casecmp /