Do not check for GOPATH env for builds (minio#5628)

Since go1.8 GOPATH is not required to set prior, as
it defaults to "${HOME}/go" we only need to check if
go tool detected GOPATH correctly. If yes then we
proceed if not we fail.

buildscripts/checkdeps.sh

@@ -128,12 +128,6 @@ assert_check_golang_env() {
         echo "Go runtime version '${installed_go_version}' is unsupported. Minimum supported version: ${GO_VERSION} to compile."
         exit 1
     fi
-
-    if [ -z "${GOPATH}" ]; then
-        echo "GOPATH environment variable missing, please refer to Go installation document at https://docs.minio.io/docs/how-to-install-golang"
-        exit 1
-    fi
-
 }
 
 assert_check_deps() {

buildscripts/checkgopath.sh

@@ -1,6 +1,6 @@
 #!/usr/bin/env bash
 #
-# Minio Cloud Storage, (C) 2015, 2016 Minio, Inc.
+# Minio Cloud Storage, (C) 2015-2018 Minio, Inc.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -16,7 +16,8 @@
 #
 
 main() {
-    IFS=':' read -r -a paths <<< "$GOPATH"
+    gopath=$(go env GOPATH)
+    IFS=':' read -r -a paths <<< "$gopath"
     for path in "${paths[@]}"; do
         minio_path="$path/src/github.com/minio/minio"
         if [ -d "$minio_path" ]; then
@@ -27,7 +28,7 @@ main() {
     done
 
     echo "ERROR"
-    echo "Project not found in ${GOPATH}."
+    echo "Project not found in ${gopath}."
     echo "Follow instructions at https://github.com/minio/minio/blob/master/CONTRIBUTING.md#setup-your-minio-github-repository"
     exit 1
 }