Improve performance of Gemfile.lock ignore check for BundleAudit hook (sds#531)

* Improve performance of Gemfile.lock ignore check

Listing ignored files in repositories with a lot of ignored files (such
as build artifcats) can take a long time.

* Split Gemfile.lock check over multiple lines

Author: jlogsdon

lib/overcommit/hook/pre_commit/bundle_audit.rb

@@ -7,7 +7,8 @@ class BundleAudit < Base
 
     def run
       # Ignore if Gemfile.lock is not tracked by git
-      ignored_files = execute(%w[git ls-files -o -i --exclude-standard]).stdout.split("\n")
+      ignored_files = execute(%W[git ls-files -o -i --exclude-standard -- #{LOCK_FILE}]).
+                      stdout.split("\n")
       return :pass if ignored_files.include?(LOCK_FILE)
 
       result = execute(command)

spec/overcommit/hook/pre_commit/bundle_audit_spec.rb

@@ -27,7 +27,7 @@
     end
 
     before do
-      subject.stub(:execute).with(%w[git ls-files -o -i --exclude-standard]).
+      subject.stub(:execute).with(%w[git ls-files -o -i --exclude-standard -- Gemfile.lock]).
         and_return(double(stdout: ''))
       subject.stub(:execute).with(%w[bundle-audit]).and_return(result)
     end