golangci-lint: enable gosec

Also exclude G115 until the following issue is resolved.

securego/gosec#1212

Author: dnaeon

.golangci.yaml

@@ -7,12 +7,16 @@ linters-settings:
       - (github.com/go-kit/kit/log.Logger).Log
       - (*github.com/weaveworks/common/logging.Level).Set
       - (*github.com/cortexproject/cortex/pkg/util/flagext.URLValue).Set
+  gosec:
+    excludes:
+      - G115
 
 linters:
   disable:
   - unused
   enable:
   - revive
+  - gosec
 
 
 issues:
@@ -44,4 +48,4 @@ issues:
     - ".*\\.pb\\.go$"
     - ".*/out_vali\\.go$"
     - ".*/.*_test\\.go$"
-    - "tests/.*"
+    - "tests/.*"