Include header info in import report (#83)

`extra_headers` now shows up in the report returned by `run!`

Author: Joe Marty

lib/csv_importer.rb

@@ -94,7 +94,7 @@ def valid_header?
   def run!
     if valid_header?
       @report = Runner.call(rows: rows, when_invalid: config.when_invalid,
-                            after_save_blocks: config.after_save_blocks)
+                            after_save_blocks: config.after_save_blocks, report: @report)
     else
       @report
     end