title: Using gganimate with geom_point and geom_line
body: <p>working with nfl data here.. trying gganimate for the first time... trying to use geom_point and geom_line but geom_line will not appear..</p>
  
  <p>data frame here..</p>
  
  <pre><code>week = c(1,2,3,4,5,6,8,9,10,11,12,13,14,15,16,17)
  plays= c(9,10,5,3,4,4,3,5,6,5,11,12,6,11,7,3)
  mean_epa= c(.67, .27, -.5, -1.09, -.3, .68, -.72, -.32, 1.03, 1.05, .56, .17, -.61, -.05, -.14, 1.5)
  CLEdrive1b &lt;- data.frame(week,plays,mean_epa)
  </code></pre>
  
  <p>within week variable, 7 is missing (because browns did not have game week 7)... not sure if that is causing issues?</p>
  
  <p>my first attempt below</p>
  
  <pre><code>p &lt;- ggplot(CLEdrive1b, aes(x=as.factor(week),y=mean_epa)) +
    theme_minimal() +
    geom_point(aes(group = seq_along(week)), color = "orange", size = 4) +
    geom_line(alpha = 0.5)+
    transition_reveal(week)+
    geom_text(aes(label = mean_epa))+
    xlab("Week") +
    ylab("EPA/Play") +
    labs(title="Browns Opening Drives",
         subtitle = "EPA/Drive by Week",
         caption="Data from nflscrapR")+
    theme(axis.title = element_text(size = 10),
          axis.text = element_text(size = 9),
          plot.title = element_text(size = 15),
          plot.subtitle = element_text(size = 10),
          plot.caption = element_text(size = 8))
  
  animate(p)
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/9NS0v.gif" alt="result for above code"></p>
  
  <p>alternative method I tried..   </p>
  
  <pre><code>pi &lt;- ggplot(CLEdrive1b, aes(week,y=mean_epa)) +
    theme_minimal() +
    geom_point(aes(group = seq_along(week)), color = "orange", size = 4) +
    geom_line(alpha = 0.5)+
    transition_reveal(week)+
    geom_text(aes(label = mean_epa))+
    xlab("Week") +
    ylab("EPA/Play") +
    labs(title="Browns Opening Drives",
         subtitle = "EPA/Drive by Week",
         caption="Data from nflscrapR")+
    theme(axis.title = element_text(size = 10),
          axis.text = element_text(size = 9),
          plot.title = element_text(size = 15),
          plot.subtitle = element_text(size = 10),
          plot.caption = element_text(size = 8))
  
  animate(pi)
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/O7iQ7.gif" alt="result for alternative method"></p>
  
  <p>removed as.factor from x variable (week).. and geom_line appears! but x-axis loses labels I am seeking and geom_text stops performing how it was above..</p>
  
  <p>thank you for spending time to help...</p>