Drop support for Go 1.11.

The protobuf 1.3.3 depends on Go interpreter of at least 1.12. Per the
Go version support policy (two releases before the current release of
1.14), this version is unsupported anyway. This commit drops support for
1.11 and expands the test matrix to cover 1.13 and 1.14.

.travis.yml

@@ -3,18 +3,18 @@ sudo: false
 
 matrix:
   include:
-    - go: "1.9"
-    - go: "1.10"
-    - go: "1.11"
-      env:
-      - GO111MODULE=off
-      - VET=1
-    - go: "1.11"
-      env: GO111MODULE=on
     - go: "1.12"
       env: GO111MODULE=off
     - go: "1.12"
       env: GO111MODULE=on
+    - go: "1.13"
+      env: GO111MODULE=off
+    - go: "1.13"
+      env: GO111MODULE=on
+    - go: "1.14"
+      env: GO111MODULE=off
+    - go: "1.14"
+      env: GO111MODULE=on
     - go: tip
 
 script:

Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.11.10-alpine as builder
+FROM golang:1.13.8-alpine as builder
 MAINTAINER FullStory Engineering
 
 # currently, a module build requires gcc (so Go tool can build
@@ -17,7 +17,6 @@ COPY cmd /tmp/fullstorydev/grpcurl/cmd
 ENV CGO_ENABLED=0
 ENV GOOS=linux
 ENV GOARCH=amd64
-ENV GO111MODULE=on
 RUN go build -o /grpcurl \
     -ldflags "-w -extldflags \"-static\" -X \"main.version=$(cat VERSION)\"" \
     ./cmd/grpcurl

go.mod

@@ -1,6 +1,6 @@
 module github.com/fullstorydev/grpcurl
 
-go 1.14
+go 1.13
 
 require (
 	github.com/golang/protobuf v1.3.3