Fix heading capitalization.

Author: ztangent

docs/src/tutorials/modeling_in_gen.md

@@ -532,7 +532,7 @@ Write an inference program that generates traces of `sine_model` that explain th
 
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-## Predicting new data
+## Predicting New Data
 
 What if we'd want to predict `ys` given `xs`?
 
@@ -786,7 +786,7 @@ Plots.plot(fixed_noise_plot, inferred_noise_plot)
 
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-## Calling other generative functions
+## Calling Other Generative Functions
 
 In addition to making random choices, generative functions can invoke other
 generative functions. To illustrate this, we will write a probabilistic model
@@ -929,7 +929,7 @@ Hint: To estimate the posterior probability that the data was generated by the s
 
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-## Modeling with an unbounded number of parameters
+## Modeling with an Unbounded Number of Parameters
 
 Gen's built-in modeling language can be used to express models that use an
 unbounded number of parameters. This section walks you through development of