Fix .travis.yml for go-modules, bump minimum Go version to 1.11 becau…

…se Gin requires http.SameSite, only supported in 1.11 onwards

.travis.yml

@@ -1,19 +1,13 @@
 language: go
 
 go:
-  - 1.7.x
-  - 1.8.x
-  - 1.9.x
-  - 1.10.x
   - 1.11.x
+  - 1.12.x
+  - 1.13.x
+  - 1.14.x
+  - 1.15.x
   - tip
 
-install:
-  - go get github.com/gin-gonic/gin
-  - go get github.com/opentracing/opentracing-go
-  - go get github.com/uber/jaeger-client-go
-  - go get github.com/uber/jaeger-client-go/zipkin
-
 script:
   - test -z $(gofmt -l .)
   - go test -v -cover -race ./...