Upgrade to using golang 1.15 to build (#240)

.travis.yml

@@ -15,6 +15,8 @@ matrix:
       - VET=1
     - go: 1.14.x
       env: GO111MODULE=on
+    - go: 1.15.x
+      env: GO111MODULE=on
     - go: tip
       env: GO111MODULE=on
 

Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.13-alpine as builder
+FROM golang:1.15-alpine as builder
 MAINTAINER FullStory Engineering
 
 # create non-privileged group and user

go.mod

@@ -1,6 +1,6 @@
 module github.com/fullstorydev/grpcurl
 
-go 1.13
+go 1.15
 
 require (
 	github.com/golang/protobuf v1.4.2