title: Problem with many (>50) states in gganimate
body: <p>I'm trying to create a GIF using <code>gganimate</code> for a data set covering 90 years, i.e. I want to have a GIF running through 90 states/years. However, it seems like <code>gganimate</code> is only able to deal with less than 50 states.</p>
  
  <p>So here's an example:</p>
  
  <pre><code>library(tidyverse)
  # devtools::install_github('thomasp85/gganimate')
  library(gganimate)
  
  df = expand.grid(  x = 1,
                     y = c(2,3),
                  year = 1670:1760) %&gt;% mutate( z = 0.03* year,
                                                u = .2 * year)
  </code></pre>
  
  <p>this all works fine for 49 years: </p>
  
  <pre><code>ggplot(data=df %&gt;% filter(., year %in% 1670:1719) , aes()) + 
    geom_point( aes(x = x, y = y, fill = z, size = u), shape = 21 ) + 
    labs( title = 'Year: {closest_state}') +
    enter_appear() +
    transition_states(year, transition_length = 1, state_length = 2) 
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/pGnik.gif" alt="example1"></p>
  
  <p>Yet, it gets weird when I include 50 (or more) years:</p>
  
  <pre><code>ggplot(data=df %&gt;% filter(., year %in% 1670:1720) , aes()) + 
    geom_point( aes(x = x, y = y, fill = z, size = u), shape = 21 ) + 
    labs( title = 'Year: {closest_state}') +
    enter_appear() +
    transition_states(year, transition_length = 1, state_length = 2) 
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/hvF3C.gif" alt="example2"></p>
  
  <p>How can I create a GIF for all 90 years? Any ideas are welcome!<br>
  I'm still new to <code>gganimate</code>, am I using <code>transition_states</code> incorrectly?  </p>