Update go in tests and Dockerfile

Some other dockerfile changes for cross compilation support and making
it easier to swap out the build image/go-version.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

.github/workflows/test.yml

@@ -2,33 +2,32 @@ name: Go
 
 on:
   push:
-    branches: [ master ]
+    branches: [master]
   pull_request:
-    branches: [ master ]
+    branches: [master]
 
 jobs:
-
   test:
     name: Build
     strategy:
       matrix:
-        go-version: [1.13.x, 1.15.x, 1.16.x]
+        go-version: [1.13.x, 1.15.x, 1.16.x, 1.17.x, 1.18.x]
         platform: [ubuntu-20.04]
     runs-on: ${{ matrix.platform }}
     steps:
-    - name: Install Go
-      uses: actions/setup-go@v3
-      with:
-        go-version: ${{ matrix.go-version }}
+      - name: Install Go
+        uses: actions/setup-go@v3
+        with:
+          go-version: ${{ matrix.go-version }}
 
-    - name: Check out code into the Go module directory
-      uses: actions/checkout@v3
+      - name: Check out code into the Go module directory
+        uses: actions/checkout@v3
 
-    - name: Build
-      run: go build -v ./...
+      - name: Build
+        run: go build -v ./...
 
-    - name: Test
-      run: go test -v ./...
+      - name: Test
+        run: go test -v ./...
 
   lint:
     runs-on: ubuntu-20.04

Dockerfile

@@ -1,7 +1,19 @@
-FROM golang:1.8 AS build
+ARG GO_VERSION=1.18
+ARG GO_IMAGE=golang:${GO_VERSION}
+
+FROM --platform=$BUILDPLATFORM $GO_IMAGE AS build
 COPY . /go/src/github.com/cpuguy83/go-md2man
 WORKDIR /go/src/github.com/cpuguy83/go-md2man
-RUN CGO_ENABLED=0 go build
+ARG TARGETOS
+ARG TARGETARCH
+ARG TARGETVARIANT
+RUN \
+    export GOOS="${TARGETOS}"; \
+    export GOARCH="${TARGETARCH}"; \
+    if [ "${TARGETARCH}" = "arm" ] && [ "${TARGETVARIANT}" ]; then \
+    export GOARM="${TARGETVARIANT#v}"; \
+    fi; \
+    CGO_ENABLED=0 go build
 
 FROM scratch
 COPY --from=build /go/src/github.com/cpuguy83/go-md2man/go-md2man /go-md2man