.travis.yml: bump to Go 1.11, use 'gofmt -s' (gregjones#92)

* .travis.yml: Bump to modern Go (1.11)

Go 1.11 came out in August [1], which means Go 1.9 and earlier are no
longer supported [2].  Just test on supported versions.

[1]: https://golang.org/doc/devel/release.html#go1.11
[2]: https://golang.org/doc/devel/release.html#policy

* Revert "Remove simplify-code option, for now"

This reverts commit be6978e (Remove
simplify-code option, for now, 2016-03-12, gregjones#40).  I expect this was
due to a simplification change between Go versions (the commit message
doesn't say), but none of the versions which we were using back then
are supported any more.

* httpcache: Update gofmt

Generated with:

  $ gofmt -s -w *.go */*.go

using:

  $ go version
  go version go1.11.2 linux/amd64

* .travis.yml: Only run 'gofmt' on 1.11.x

The indent heuristic changed with Go 1.11 [1], so there's no single
form that satisfies gofmt for both Go 1.10 and Go 1.11.  With this
commit, we now only run gofmt on 1.11.

Docs for the 'include' syntax are in [2].

Also replace the double-diff with a 'gofmt -w ...' to write the
changes and a 'git diff ...' call to display the changes and exit
non-zero if there were any.

[1]: https://golang.org/doc/go1.11#gofmt
[2]: https://docs.travis-ci.com/user/customizing-the-build/#explicitly-including-jobs

Author: wking

.travis.yml

@@ -1,19 +1,18 @@
 sudo: false
 language: go
-go:
-  - 1.6.x
-  - 1.7.x
-  - 1.8.x
-  - 1.9.x
-  - master
 matrix:
   allow_failures:
     - go: master
   fast_finish: true
+  include:
+    - go: 1.10.x
+    - go: 1.11.x
+      env: GOFMT=1
+    - go: master
 install:
   - # Do nothing. This is needed to prevent default install action "go get -t -v ./..." from happening here (we want it to happen inside script step).
 script:
   - go get -t -v ./...
-  - diff -u <(echo -n) <(gofmt -d .)
+  - if test -n "${GOFMT}"; then gofmt -w -s . && git diff --exit-code; fi
   - go tool vet .
   - go test -v -race ./...

httpcache.go

@@ -416,14 +416,14 @@ func canStaleOnError(respHeaders, reqHeaders http.Header) bool {
 func getEndToEndHeaders(respHeaders http.Header) []string {
 	// These headers are always hop-by-hop
 	hopByHopHeaders := map[string]struct{}{
-		"Connection":          struct{}{},
-		"Keep-Alive":          struct{}{},
-		"Proxy-Authenticate":  struct{}{},
-		"Proxy-Authorization": struct{}{},
-		"Te":                struct{}{},
-		"Trailers":          struct{}{},
-		"Transfer-Encoding": struct{}{},
-		"Upgrade":           struct{}{},
+		"Connection":          {},
+		"Keep-Alive":          {},
+		"Proxy-Authenticate":  {},
+		"Proxy-Authorization": {},
+		"Te":                  {},
+		"Trailers":            {},
+		"Transfer-Encoding":   {},
+		"Upgrade":             {},
 	}
 
 	for _, extra := range strings.Split(respHeaders.Get("connection"), ",") {
@@ -433,7 +433,7 @@ func getEndToEndHeaders(respHeaders http.Header) []string {
 		}
 	}
 	endToEndHeaders := []string{}
-	for respHeader, _ := range respHeaders {
+	for respHeader := range respHeaders {
 		if _, ok := hopByHopHeaders[respHeader]; !ok {
 			endToEndHeaders = append(endToEndHeaders, respHeader)
 		}