reviewdog: ignore underscores in package names (elastic#4015)

Unfortunately this is the best we can do between golint and reviewdog:

golang/lint#98 (comment)

Author: 7AC

reviewdog.yml

@@ -1,3 +1,3 @@
 runner:
   golint:
-    cmd: golint $(go list ./... | grep -v /vendor/)
+    cmd: golint $(go list ./... | grep -v /vendor/) | grep -v "don't use an underscore in package name"