title: Rubocop guard clause dilemma - unnecessary if else VS line too long guard clause
body: <p>I have this piece of code where I have a raise statement with a guard clause:</p>
  
  <pre><code>def validate_index index
    # Change to SizeError
    raise ArgumentError, "Size of index (#{index.size}) does not matches"\
      "size of vector (#{size})" if size != index.size
  end
  </code></pre>
  
  <p>On this, rubocop gives the offence:</p>
  
  <pre><code>Style/MultilineIfModifier: Favor a normal if-statement over a modifier clause in a multiline statement.
  </code></pre>
  
  <p>I modified my code to this to normal if else case as this:</p>
  
  <pre><code>def validate_index index
    # Change to SizeError
    if size != index.size
      raise ArgumentError, "Size of index (#{index.size}) does not matches"\
        "size of vector (#{size})"
    end
  end
  </code></pre>
  
  <p>But now it gives this offence:</p>
  
  <pre><code>Style/GuardClause: Use a guard clause instead of wrapping the code inside a conditional expression.
  </code></pre>
  
  <p>What to do in such case? Both are raising errors. Any other alternative?</p>