title: "Error: Provided file does not exist" when using gganimate with lines
body: <p>As a followup to <a href="https://stackoverflow.com/questions/60820794/using-gganimate-and-getting-all-kind-of-errors/60821350#60821350">this question</a>, I tried, as suggested by <a href="https://stackoverflow.com/questions/60820794/using-gganimate-and-getting-all-kind-of-errors/60821350#comment107609418_60820794">a comment</a>, to use <code>geom_line</code> and <code>transition_reveal</code>. Since using several <code>geom_line</code> statements seemed to clash with gganimate (giving warnings about using a single element in a group and not rendering anything) I tried to gather everything into a single column and a single ggplot2 statement, here. </p>
  
  <pre><code>library(ggplot2)
  library(transformr)
  library(gifski)
  library(gganimate)
  library(tidyr)
  
  load("covid-19-es.Rda")
  data &lt;- gather(data,Tipo,Cuantos,c(casos,salidas))
  my_plot &lt;- ggplot(data,aes(x = Fecha, y = Cuantos, group= Tipo, color=Tipo)) + 
    geom_line() +
    transition_reveal(Fecha) + ease_aes("linear")+
    labs(title='Day: {closest_state}')
  
  animate(
    plot = my_plot,
    render = gifski_renderer(),
    height = 600,
    width = 800, 
    duration = 10,
    fps = 20)
  
  anim_save('gifs/casos-salidas-linea.gif')
  </code></pre>
  
  <p>The data file used is <a href="https://github.com/JJ/covid-reports/blob/master/covid-19-es.Rda" rel="nofollow noreferrer">here</a>. I'm getting lots of warning when using animate, but it's finally killed with the unhelpful message (again):</p>
  
  <pre><code>Error: Provided file does not exist
  </code></pre>
  
  <p>At the end of the day, what I need is to animate line charts with <code>ggplot2</code>. If there's any other method, it'll be very wellcome </p>
  
  <p>Versions used</p>
  
  <ul>
  <li>R 3.6</li>
  <li>ggplot 2_3.3.0</li>
  <li>gganimate 1.0.5</li>
  <li>gifski 0.8.6</li>
  </ul>