CODE: build_aho_corasick_graph! bug fix

* This patch fixes a bug in the build_aho_corasick_graph! function.
* The build_aho_corasick_graph! can get ONLY a list of keywords.
* In case we need to read the keywords from a file the procedure is
  the follows
    - lines = File.readlines(“file-path”).map(&:strip)
  the strip function gets rid of leading and trailing spaces