minor #3584 Fix emphasis on compiler to bold styling (jonnyeom)

This PR was submitted for the 2.x branch but it was merged into the 1.x branch instead.

Discussion
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Fix emphasis on compiler to bold styling

This is just so the Lexer, Parser, and Compiler has the same styling

Commits
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97ae3c8 Fix emphasis on compiler to bold styling

doc/internals.rst

@@ -20,7 +20,7 @@ The rendering of a Twig template can be summarized into four key steps:
   * Then, the **parser** converts the token stream into a meaningful tree
     of nodes (the Abstract Syntax Tree);
 
-  * Finally, the *compiler* transforms the AST into PHP code.
+  * Finally, the **compiler** transforms the AST into PHP code.
 
 * **Evaluate** the template: It means calling the ``display()``
   method of the compiled template and passing it the context.