chore(go): update project for go 1.16 (modules, etc)

Dockerfile

@@ -1,18 +1,14 @@
-FROM golang:1.10-alpine as builder
-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
-ADD . /go/src/github.com/jimeh/casecmp
-RUN set -e \
-    && dep ensure \
-    && CGO_ENABLED=0 go build -a -o /casecmp \
-       -ldflags "-s -w \
-          -X main.version=$(cat VERSION) \
-          -X main.commit=$(git show --format='%h' --no-patch)\
-          -X main.date=$(date +%Y-%m-%dT%T%z)"
+FROM golang:1.16-alpine as builder
+RUN apk add --no-cache \
+    git
 
+WORKDIR /app
+COPY . /app
+RUN env CGO_ENABLED=0 \
+    go build -a -o /casecmp -ldflags "-s -w \
+        -X main.version=$(cat VERSION) \
+        -X main.commit=$(git show --format='%h' --no-patch) \
+        -X main.date=$(date +%Y-%m-%dT%T%z)"
 
 FROM scratch
 COPY --from=builder /casecmp /