chore(deps): update all docker tags

Dockerfile

@@ -1,5 +1,5 @@
 # build
-FROM            golang:1.14-alpine as builder
+FROM            golang:1.15-alpine as builder
 RUN             apk add --no-cache git gcc musl-dev make
 WORKDIR         /go/src/github.com/moul/gotty-client
 COPY            go.* ./
@@ -8,6 +8,6 @@ COPY            . ./
 RUN             make install
 
 # minimal runtime
-FROM            alpine:3.11
+FROM            alpine:3.12
 COPY            --from=builder /go/bin/gotty-client /bin/
 ENTRYPOINT      ["/bin/gotty-client"]