switch to go 1.13 and latest linter

.golangci.yml

@@ -69,4 +69,4 @@ issues:
   exclude-use-default: false
 
 service:
-  golangci-lint-version: 1.15.x
+  golangci-lint-version: 1.19.x

.travis.yml

@@ -4,21 +4,21 @@ services:
   - mongodb
 
 go:
-  - "1.12.x"
+  - "1.13.x"
 
 install: true
 
 before_install:
   - export TZ=America/Chicago
-  - curl -sfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh| sh -s -- -b $(go env GOPATH)/bin v1.17.1
+  - curl -sfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh| sh -s -- -b $(go env GOPATH)/bin v1.19.1
   - golangci-lint --version
   - go get github.com/mattn/goveralls
   - export MONGO_TEST=mongodb://127.0.0.1:27017
   - export PATH=$(pwd)/bin:$PATH
 
 script:
-  - GO111MODULE=on go get ./...
-  - GO111MODULE=on go mod vendor
-  - GO111MODULE=on go test -v -mod=vendor -covermode=count -coverprofile=profile.cov ./... || travis_terminate 1;
+  - go get ./...
+  - go mod vendor
+  - go test -v -mod=vendor -covermode=count -coverprofile=profile.cov ./... || travis_terminate 1;
   - golangci-lint run --tests=false  || travis_terminate 1;
   - $GOPATH/bin/goveralls -coverprofile=profile.cov -service=travis-ci