chore(backend): use Go 1.11.5 everywhere

.travis.yml

@@ -1,6 +1,6 @@
 defaults_go: &DEFAULTS_GO
   language: go
-  go: "1.11.4"
+  go: "1.11.5"
   cache:
     directories:
       # https://restic.net/blog/2018-09-02/travis-build-cache

demo/Dockerfile

@@ -3,7 +3,7 @@ RUN apk add --update make git
 COPY . /karma
 RUN make -C /karma ui
 
-FROM golang:1.11.4-alpine as go-builder
+FROM golang:1.11.5-alpine as go-builder
 COPY --from=nodejs-builder /karma /go/src/github.com/prymitive/karma
 ARG VERSION
 RUN apk add --update make git