Downgrade golangci-lint version

Until golangci/golangci-lint#827 is fixed, we
shuold use a more stable version instead.

Author: colega

.travis.yml

@@ -8,7 +8,7 @@ env:
   - GO111MODULE=on
 
 install:
-  - curl -sSfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b $(go env GOPATH)/bin v1.22.2
+  - curl -sSfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b $(go env GOPATH)/bin v1.20.1
 
 script:
   - make test