Update procedural-macros.md

Author: merelymyself

src/procedural-macros.md

@@ -53,7 +53,7 @@ type, unlike `Vec<TokenTree>`, is cheap to clone.
 All tokens have an associated `Span`. A `Span` is an opaque value that cannot
 be modified but can be manufactured. `Span`s represent an extent of source
 code within a program and are primarily used for error reporting. While you
-cannot modify a `Span` itself, you can always change the `Span` *associated* 
+cannot modify a `Span` itself, you can always change the `Span` *associated*
 with any token, such as through getting a `Span` from another token.
 
 ### Procedural macro hygiene