Disable revive linter rule package-comments (#79)

Even though the `package-comments` rule [1] of the `revive` linter [2]
is quite useful, it produces false-positive errors when another file
already has a package documentation. Duplicating documentation is not a
workaround so the rule has been disabled for now and might be re-enabled
if the rule logic gets updated.

[1]: https://github.com/mgechev/revive/blob/master/RULES_DESCRIPTIONS.md#package-comments

Closes GH-78

.golangci.yml

@@ -190,7 +190,6 @@ linters-settings:
         severity: error
       - name: increment-decrement
       - name: indent-error-flow
-      - name: package-comments
       - name: range
       - name: receiver-naming
       - name: redefines-builtin-id