input: Write a python function to summarize an article using LexRank algorithm from the sumy library.
  assert summarize_article('article.txt') is not None
  assert len(summarize_article('article.txt')) > 0
output: def summarize_article(file_path):
      from sumy.parsers.plaintext import PlaintextParser
      from sumy.nlp.tokenizers import Tokenizer
      from sumy.summarizers.lex_rank import LexRankSummarizer
  
      with open(file_path, 'r', encoding='utf-8') as file:
          article_text = file.read()
  
      parser = PlaintextParser.from_string(article_text, Tokenizer("english"))
      summarizer = LexRankSummarizer()
  
      summary = summarizer(parser.document, 5)  # Summarize the document into 5 sentences
      summary_text = ' '.join(str(sentence) for sentence in summary)
  
      return summary_text