Should not mention filename in error output

[swernerx]

Currently the plugin is not just mentioning the error message itself but also adds the filename.

64:19  warning  Generic Object Injection Sink: /Users/sebastian/Workspace/sebastian-software/edgestack/src/webpack/ConfigFactory.js: 64
              copy[key] = obj[key]

                             security/detect-object-injection

which actually makes a lot of noise compared to other eslint checks.

ESLint already lists exactly the same issue location as the one mentioned in the message. So this is duplicate information.

[pdehaan]

Attempted PR at #17.