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.

.travis.yml

@@ -12,6 +12,6 @@ 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 .)
+  - diff -u <(echo -n) <(gofmt -d -s .)
   - go tool vet .
   - go test -v -race ./...