Update Dockerfile for go modules

Dockerfile

@@ -1,33 +1,17 @@
-FROM alpine:3.6
+FROM golang:1.11-alpine
 
-ARG version=0.4.1
-ARG buildhost=https://github.com/mwstobo/airhornbot/archive
-ARG buildfile=cmd/bot/bot.go
-ARG tar_filename=${version}.tar.gz
-
-ENV GOPATH=/root/go
-ENV AIRHORN_SRC=$GOPATH/src/github.com/mwstobo/airhornbot
+WORKDIR /opt/airhornbot
+COPY . .
 
 RUN apk update \
- && apk add --no-cache \
-            ca-certificates \
  && apk add --no-cache \
             --virtual build \
-            wget \
-            go \
-            glide \
+            gcc \
             git \
-            musl-dev \
- && update-ca-certificates \
- && wget ${buildhost}/${tar_filename} \
- && mkdir -p $AIRHORN_SRC \
- && tar xvf "${tar_filename}" -C $AIRHORN_SRC --strip 1 \
- && rm "${tar_filename}" \
- && cd $AIRHORN_SRC \
- && glide install \
- && go build ${buildfile} \
+            musl-dev
+
+RUN go mod vendor \
+ && go build cmd/bot/bot.go \
  && apk del build
 
-WORKDIR $AIRHORN_SRC
-CMD ["./bot", \
-       "-t YOUR_TOKEN_HERE"]
+CMD ["./bot", "-t YOUR_TOKEN_HERE"]