chore(golang): use Go 1.11 when testing and building Docker images

.travis.yml

@@ -1,6 +1,6 @@
 defaults_go: &DEFAULTS_GO
   language: go
-  go: "1.10.3"
+  go: "1.11"
   cache:
     directories:
       - vendor

Dockerfile

@@ -3,7 +3,7 @@ RUN apk add --update make git
 COPY . /unsee
 RUN make -C /unsee ui
 
-FROM golang:1.10.3-alpine as go-builder
+FROM golang:1.11.0-alpine as go-builder
 COPY --from=nodejs-builder /unsee /go/src/github.com/prymitive/unsee
 ARG VERSION
 RUN apk add --update make git