Refactor Bundler::Audit::Scanner#initialize

[postmodern]

Looking at #initialize now, it seems that it should accept the scanner options (:ignore) and store those as instance variables. The #scan method would then accept the path to the Gemfile.lock. This would allow the Scanner object to be configured once and ran across multiple Gemfile.lock files.

[postmodern]

Would this be relevant to @mveytsman and @phillmv's interests?

[picatz]

This may be partially related to #182

[daveallie]

Interested in this. Working through the process of upgrading a production app, and currently have the app booting 2 versions of Rails. Each version is run off different bundler lockfiles, Gemfile.lock, and GemfileNext.lock. Would love for a way to supply a list of lockfiles to check or just basic cli support for custom lockfile path. If you're interested in the latter (even though it will most likely clash with this issue), please let me know and I'll submit a PR.

[postmodern]

@daveallie Linking my comment on scanning multiple Gemfile.lock in one go vs. multiple CI runs:
#224 (comment)