Skip the code feedback intro if it's too long

[gadenbuie]

Fixes #202

If it's more than 80 characters, it's too long for the markdown text to be actually helpful. 80 characters is probably high but anything larger is definitely too much context.

Before

ex <- mock_this_exercise(
  'ggplot(data = penguins, mapping = aes(x = flipper_length_mm, fill = species)) +
    geom_density(alpha = 0.4) + 
    labs(title = "Gentoos have the longest flippers", x = "Flipper length (mm)", y = "Density") + 
    scale_color_brewer(palette = "Set1")',
  'ggplot(data = penguins, mapping = aes(x = flipper_length_mm, fill = species)) +
    geom_density(alpha = 0.4) + 
    labs(title = "Gentoos have the longest flippers", x = "Flipper length (mm)", y = "Density") + 
    scale_fill_brewer(palette = "Set1")'
)

code_feedback(ex$.user_code, ex$.solution_code)

In ggplot(data = penguins, mapping = aes(x = flipper_length_mm, fill = species)) + geom_density(alpha = 0.4) + labs(title = "Gentoos have the longest flippers", x = "Flipper length (mm)", y = "Density") + scale_color_brewer(palette = "Set1"), I expected you to call scale_fill_brewer() where you called scale_color_brewer().

After

code_feedback(ex$.user_code, ex$.solution_code)

I expected you to call scale_fill_brewer() where you called scale_color_brewer().