[build] Only build from latest.

.travis.yml

@@ -3,6 +3,7 @@ sudo: false
 matrix:
   include:
     - go: 1.x
+      env: LATEST=true
     - go: 1.5
     - go: 1.6
     - go: 1.7
@@ -21,7 +22,8 @@ script:
   - diff -u <(echo -n) <(gofmt -d .)
   - go vet $(go list ./... | grep -v /vendor/)
   - go test -v -race ./...
-  - gox -os="linux darwin windows" -arch="amd64" -output="logshare.{{.OS}}.{{.Arch}}" -verbose ./...
+  # Only build binaries from the latest Go release.
+  - if [ "${LATEST}" = "true" ]; then gox -os="linux darwin windows" -arch="amd64" -output="logshare.{{.OS}}.{{.Arch}}" -verbose ./...; fi
 
 deploy:
   provider: releases
@@ -35,3 +37,4 @@ deploy:
   on:
     repo: cloudflare/logshare
     tags: true
+    condition: $LATEST = true