chore: update instructions and Dockerbuild to work with modules

.dockerignore

@@ -0,0 +1 @@
+.git

Dockerfile

@@ -1,12 +1,16 @@
 # Docker image for the Drone Terraform plugin
 #
 #     docker build -t jmccann/drone-terraform:latest .
-FROM golang:1.10-alpine AS builder
-COPY ./*.go ./src/
-COPY ./vendor/ ./src/
-RUN set -ex \
-    && cd ./src \
-    && CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -a -tags netgo -o /go/bin/drone-terraform
+FROM golang:1.11-alpine AS builder
+
+RUN apk add --no-cache git
+
+RUN mkdir -p /tmp/drone-terraform
+WORKDIR /tmp/drone-terraform
+COPY . .
+
+RUN go mod download
+RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -a -tags netgo -o /go/bin/drone-terraform
 
 FROM alpine:3.7
 

README.md

@@ -10,8 +10,10 @@ a listing of the available options please take a look at [the docs](https://gith
 Build the binary with the following commands:
 
 ```
-go build
+export GO111MODULE=on
+go mod download
 go test
+go build
 ```
 
 ## Docker
@@ -19,18 +21,9 @@ go test
 Build the docker image with the following commands:
 
 ```
-CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -a -tags netgo
 docker build --rm=true -t jmccann/drone-terraform .
 ```
 
-Please note incorrectly building the image for the correct x64 linux and with
-GCO disabled will result in an error when running the Docker image:
-
-```
-docker: Error response from daemon: Container command
-'/bin/drone-terraform' not found or does not exist.
-```
-
 ## Usage
 
 Execute from the working directory: